How to possibly prevent cylinder scoring - Page 5 - Porsche General - PistonHeads UK

Although our low temperature thermostat is something that we think could make these engines less likely to score bores - I have also been trying hard to work out what driving conditions might be more likely to lead to scored bores in the first place – to be able to offer some advice on how best to avoid the consequences. Feedback suggests it is not people driving around in track situations that are particularly any more likely to experience this problem than anyone else – so it does not seem to be purely down to revs and hard driving entirely. Furthermore – for those only ever driving on public roads - for some to fail so soon while others never seem to – or when some owners never have the problem while others do – there must be some differences - and if we could identify them (and back them up with technical/scientific support) it could possibly help avoid the consequences altogether. I think I may have worked out a typical scenario – best avoided – here is the evidence and connected technical issues. Scoring was more commonly caused by full piston seizures in which the piston grew too big to fit in the bore with some clearance and the resulting additional force between the piston and cylinder wall squeezed out the oil film resulting in metal to metal contact – the increased friction causing local melting of the piston surface and scoring both piston and bore on both sides. Dynamometer tests I have previously carried out to destruction (to measure temperatures etc) showed this cycle took about 4-5 seconds. The odd thing about this current problem is that one side of the piston and bore looks exactly like a fully scored seized piston but the other side is perfectly OK and untouched. It is therefore clear that when the scoring occurs – one side of the piston is sufficiently cool to lubricate the piston/bore face and support the piston whereas the other side has become excessively hot and the oil film cannot support the loads applied – which result in metal to metal contact – overheating of the surface and scoring the bores and piston on one side only. It is always the thrust side that scores (proving the additional load between the piston and cylinder wall is the problem) but it cannot be the piston temperature overall – or the other side would also seize. Although the thermostat controls overall coolant speed (from the radiator efficiency) the coolant flow in individual parts of these blocks is much slower than traditional engine designs (because it is split into 12 separate flows streams instead of one (each therefore at least 1/12 of the speed) – the 6 through the block being very much slower than the 6 through the cylinder heads and the individual speed past any one cylinder many times slower) so the temperature of the coolant as it slowly passes over the outer cylinder wall increases more giving a greater temperature rise in any one area. It is almost always bank 2 (because on that bank the thrust face is on the hottest side of the block – as the coolant is about to leave the cylinder having picked up all the heat on its travel through the block - whereas on bank 1 the coolest coolant enters on the thrust side). For the cylinder wall to get so hot on one side that the engine piston scores must require (IMHO) some bubbling of the coolant on the surface of the outer cylinder wall and this usually only occurs when coolant speeds would be very slow indeed and bubbles would naturally rise to the top (the thrust side on bank 2 – not on bank 1). But it would also need high piston to cylinder wall forces as well to squeeze out the oil film and make hard contact between the piston and Lokasil bore. Centrifugal coolant pumps have relatively low pumping speeds until they reach a critical speed after which they suddenly increase flow dramatically. Radiators cool more when the road speed is higher (when their efficiency increases). The engines in question (3.4 Cayman S, 996 and 997 3.6 and 3.8) produce more torque at low revs than their predecessors. There is a piston cooling affect from inlet charge when the throttle is open momentarily lost as the throttle is closed. Spray jets in the block lubricate the cylinder wall but have ball valves that require some oil pressure to open and the oil pressure and delivery is low at low revs – rising until the pressure relief valve opens when it is constant at much higher pressure and delivery providing much better cylinder wall lubrication. Crankshaft speed also distributes more cylinder oil spray at higher speeds. The relatively long distance from the engine to the radiators reduces cooling reaction time. The thermostat is on the way back to the engine so if the engine is ticking over after a run the cooler coolant that has just come from the radiator will slow down as it reaches the thermostat and for a while – will not encourage it to open more – in fact it would probably start to shut a little. Putting all this together – if we had a scenario in which the engine was under quite high load and road speed but then it suddenly went to tickover speed for a short while – at this point the piston would be very hot (no inlet charge), the coolant speed would be very low (pump slow), the heat passing from the cylinder outer wall to the coolant would still be high (probably leading to bubbling which is very poor for heat dissipation), the oil spray cylinder wall jets output and crankshaft rotational speed would be very low (so reduced cylinder wall lubrication) and while the coolant in the block would be very hot the coolant near the thermostat would be quite cool. If just then the car was driven off under high torque/full or nearly full throttle (not necessarily at high revs) the pistons would instantaneously heat up, the dynamic forces between the piston and the cylinder wall would be at their highest, the cylinder wall and oil film temperature would be very high, the thermostat would not be fully open, the car would not yet be at a high enough road speed for the radiator to cool the coolant effectively and the oil spray jet and crankshaft speed splash lubrication would not yet be good. So – put simply – I think that if the owner of one of these models – on a spirited drive - could not then resist the temptation to floor the car away from standstill (at say lights or junctions) - then I think we could have the worst possible scenario for piston/cylinder scoring at that precise moment. This would also explain why – once the models are up to temperature and having had the speed gradually increased around say a circuit or long unrestricted roads (say in Germany) they seem to be OK despite the extra strain put on the engines (because thermostats are more open, radiator cooling is good, engine speed is high so oil spray etc is good et)c. I agree such a proposition is almost madness – I can almost hear you all shouting “what the bl**dy hell do you think I bought it for” - why would anyone buy such a car if they cannot at least feel that acceleration and enjoy that performance (not to mention the satisfaction of showing everyone just how quick the car is when in reality none of us can safely or legally demonstrate anything like the cars top speeds anywhere in the UK – but we can out accelerate most others). Surely that exact scenario is partly why we bought it and high on the list of the pleasure we get from driving it and possibly the only occasion we can stuff it to other drivers! I am not against that – in fact I also love it myself (truth be known). So I am not proposing you all drive around like old men in a Ford Fiesta – (I am of that age – but still not a slow driver either)but I am just suggesting that – it makes sense to me – that weighing up all the evidence and connecting it to solid technical analysis - this is the most likely moment of failure and therefore – it could be that if you could simply accelerate from a stationary rest - a little more gently – under slightly less throttle opening -for a few seconds until the coolant speed, oil pressure and thermostat opening times and the balance of the oil and lubrication system have equalised again – it may just save the expense and disappointment of an engine failure. Baz

hartech said: you all drive around like old men in a Ford Fiesta ALL 911 drivers do anyway!

Interesting Baz, unless I haven't understood you - this isn't just about RPMs, it seems some combination of 'RPMs + road speed' required before we can 'safely' WOT, yes?

So, in simple terms, is best practice not to stop at junctions...

So, if I have understood correctly, the basic cause is poor cooling at idle? Can anything be done to improve or fix? MTR Edit, apart from your suggestion regarding driving behaviour of course.

I think your theory is plausible. One thing you could look at next time you get the chance, is whether any ensuing air-pockets in the water jacket will be trapped against the bore-wall - for example if the openings in the head-gasket are not matched to the water core in the block, could they prevent the air bleeding out, particularly at idle, were the coolant isn't flowing fast enough to drag the air with it. Assuming this is Porsche's first attempt at water-cooling a flat engine, it's something they may have overlooked.

anonymous said: [redacted] I'd be surprised if : A. The orignal piston to bore specifications were that tight. and B. Modern production tolerances were that large. Sounds more like an intrinsic design fault that rears its head in certain circumstances. Are the engines being run too lean for emissions reasons ? which in turn means the pistons are running too hot and their rate of thermal expansion is inconsistent and excessive. Edited by Slippydiff on Tuesday 9th August 13:44

Are you sure the thermostat is on the coolant return to the engine. A thermostat should allow restricted flow of coolant when cool to allow the engine to warm up quickly, and also regulate engine temperature in cold weather. If the thermostat is on the return the coolant passing through the bleed hole will take absolutly agees to get hot as it has to pass through the rads in the front of the car and then back to the thermostat. Full circulation and cooling will only start once the thermostat is open, and by then the coolant temp within the engine would be really hot. Could a remote thermostat be fitted in the correct position, ie on the flow pipe from the engine where it will respond to temperature change immediatly.

Sounds like I need to start driving my 3.4 Cayman S like my sister would - get up to a terminal velocity then maintain that speed for the entire journey, oblivious to roundabout priority, junctions, traffic lights, prevailing speed limits, pedestrians, etc. Drive it like a slow but lethal train, right?

Hi, I did suggest a electronically controlled thermostat around 12 months... Like BMW use in some of their models they have what looks like a heater plug directly in front of the thermostat... When needed it superheats the coolant and forces the stat to open...would this be of some use. If you want I could offer some electrical assistance. Worth considering if you think it maybe of some use. Mike

Thanks guys I obviously don't know what I am talking about. Baz

Interesting reading Baz, well done for taking the time to explain it to us mere mortals. There is a great deal to digest, but would it be to simplistic to think that if a thicker oil was specified by Porsche then the problems would of been lessened? When you see oil being drained from a hot 996/7 (or cayman etc) then you can see how thin it gets when up to temperature, and therefore decreasing the engine oil pressure. I personally don't think the service schedule on the later cars helps the situation either, 6 monthly oil changes with a 10/60 would surely help, no? Cheers.

Hi, My car although different engine gt, I use 10w60 engine oil. Mike

Hi, My car although different engine gt, I use 10w60 engine oil. Mike

I agree and have always promoted the use of a thicker oil - despite creating a huge wave of posts dissagreeing with me. I suppose I would actually be better off ignoring publishing my concerns for owners and just fixing the increasing numbers that are failing. Baz

Baz excellent perfect storm scenario,I had a car that had on its last memorable drive before failure (just asked the owner about his last journey)been driven hard on the motorway then got caught in jam or slow moving traffic on a hot sunny day then had a bit more WOT on the way home arrived all fine. However next morning from cold start up ticking noise from one bank new engine required! NB We all appreciate these posts Baz they are so helpfull!

hartech said: I agree and have always promoted the use of a thicker oil - despite creating a huge wave of posts dissagreeing with me. I suppose I would actually be better off ignoring publishing my concerns for owners and just fixing the increasing numbers that are failing. Baz From what I'm told you already have enough work to see you into retirement ;-)

hartech said: I agree and have always promoted the use of a thicker oil - despite creating a huge wave of posts dissagreeing with me. I suppose I would actually be better off ignoring publishing my concerns for owners and just fixing the increasing numbers that are failing. Baz I for one think for a relatively small outfit all things considered are doing a fantastic job ! I don't know of anyone more knowledgable than you in this field. Mike

hartech said: I agree and have always promoted the use of a thicker oil - despite creating a huge wave of posts dissagreeing with me. I suppose I would actually be better off ignoring publishing my concerns for owners and just fixing the increasing numbers that are failing. Baz Please don't be so melodramatic Baz - many of us out here really do enjoy a lengthy technical post in terms that we can understand and also always have our independents of choice fill our cars with 10w60...

Excellent post Baz. Never let anyone on PH get you down. You keep doing your thing mate, cheers Graeme

hartech said: For the cylinder wall to get so hot on one side that the engine piston scores must require (IMHO) some bubbling of the coolant on the surface of the outer cylinder wall and this usually only occurs when coolant speeds would be very slow indeed and bubbles would naturally rise to the top (the thrust side on bank 2 – not on bank 1). But it would also need high piston to cylinder wall forces as well to squeeze out the oil film and make hard contact between the piston and Lokasil bore. How about fitting steam vents on the upper side of the block? As you may know it's a common mod on 944T that are prone to blow the headgasket on the 4th cylinder as the head has a cavity in which steam can be trapped if the system hasn't been bled correctly. On high end builds the 2V head still sees coolant turn into steam and several vents are added.

Hi Baz I am reading with interest re the engine problems that these cars suffer. I am looking at may be getting a Cayman S some time in the next 12 months and this does concern me a little. Out of interest do products like water wetter help with this kind of problem? I have raced a Westfield for the last five years with a highly modified 2000cc Vauxhall engine fitted and a small radiator to save weight. I have used water wetter to good effect keeping the engine temps under control even though the engine was making over 280bhp and a radiator designed for a 1000cc VW Polo. It's just a thought and I am sure it's already been tried. Cheers Matt

Great stuff. My own, updated 'shopping list' of ideas for simpler fixes to the issue, mostly intuitive... 1 The lower temp engine thermostat. (got this now, phew, thanks Baz) 2 An electric in line water pump to increase the coolant flow to the front radiators once the temp reaches a certain level in the front pipework. Obviously as a failsafe the pump should not restrict flow when off. No idea how to achieve all this -at the moment but the pumps exist on ebay -drag racer kit I think, for whom heat build up is a tad quick...! 3 Centre radiator for extra cooling. 4 A reduction in the temperature at which the stage 1 radiator fans cut in. No idea how to achieve it without by passing the existing circuits, which of course is an easy fix, but it would be neatest to have the cars ECU set to a lower temp, eg 95c for cooling fan start up. 5 Modified front wheel arch liners (to latest 997 GT3 design) to induce higher air flow through the front radiators at low driving speeds. Will do this soon and will probably copy the GT3 cut-out design. Also thinking about trying some guide vanes in the front face of the rad. 6 A reduction in the temperature at which the engine bay fans start up, ECU fix? 7 Faster water pump pulley -any further on investigating this Baz? 8 Increase the % water content in the coolant (water has twice the thermal capacity I hear!) Anyone got any more ideas

Here is the BMW electronic thermostat. No idea how it works, had thought it was a servo....

Some great positive and intelligent suggestions recently - most of which would/could make a difference and many would probably solve the problem - however all involve major changes to cars that do not yet have the scoring problem and the trouble is that most owners I would not expect to incurr the expense and inconvenience until it is too late when they realise perhaps they should have done. Many are blinded by the product's reputation and cannot believe the reported danger until it hits them. Indeed most don't seem to find out about all this until it is too late and research who can fix it. The take up of the low temperature thermostat has been extremely small (despite the obvious advantages, low cost and reported benefits) - so on that basis I was trying to think of something simple - that costs nothing - that owners might just hear about and manage to follow to help avoid damage - just simply to restrain themselves from too much enthusiasm on opening imediately up after a spell at rest when the engine had been used hard before the stop. Baz

911Fiddler said: Here is the BMW electronic thermostat. No idea how it works, had thought it was a servo.... Electric stats are a good idea but need a bit of controlling from an ecu. I know the VW electronic stat has sensors both side of the stat to check its operating correctly. The stat opens early when full throttle is applied to produce maximum power and when on light throttle cruising it slows its opening to run the engine hotter for better emissions. I would think a retro fit to a car could be expensive and and possibly not that easy. Still the idea is sound if it could be integrated with the can bus system so the stat knew when the car was slowing down on light throttle and could open early to allow for a cooler running temp when idling.

hartech said: ...suggestions recently - most of which would/could make a difference and many would probably solve the problem - however all involve major changes to cars... ...I was trying to think of something simple - that costs nothing - that owners might just hear about and manage to follow to help avoid damage - just simply to restrain themselves from too much enthusiasm on opening imediately up after a spell at rest... Baz I for one wouldn't consider, say, a lower-temp thermostat, third radiator, and some water-additive as major changes and would readily have these items fitted if they reduced, or better still eliminated, the likelihood of scored bores. If the 'Wetter' product really can 'reduce temps by 20degs', and reduce cavitation and bubbling, would this be enough of a temp drop (perhaps in combination with your thermostat) to cool the cylinders sufficiently? Baz, are these types of changes sufficient, do you think, to eliminate the need to avoid WOT from a standstill without the risk of cylinder/piston damage?

Baz Could you expand on the benefits of a low temp thermostat as I thought that once the car was up to temperature and the thermostat was open that it stayed open and that the only effect the low temp thermostat would have would be to slow down the time it took for the engine to get up to operating temp? Would be interested to know more about this?

Can't agree with everything you say. That low temp t-stat may not be the cure all you think it is. Tests have shown that as the engine temp goes down wear increases and fuel consumption increases. Here are some numbers: Temp Wear (cylinder) Fuel Consumption (GPH) 70F 0.008" 3.8 120F 0.002" 3.5 155F 0.001" 3.2 180F 0.0005" 2.9 210F 0.0003" 2.8 Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine. Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat. Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are precision cast into the head) are used which carry coolant from a larger passage to an adjacent but smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area (generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling. Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts. Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown. The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place. The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface. The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets. Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides. Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches. The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up. My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system. Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring. If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further. I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory. In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened. There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them. Sincerely, Rockster.

It seems to me that a third rad should be very high on the mod list for those who can. I asked my local knowledgeable parts shop today about 5w-50 but they said they'd have to order a crate in. however, they did have Castrol 10w-60, and since sportsandclassic has been using it (even for the gt engine) I think I'll give this a try in the near future. I would like to have one lot of mods, as I use my car every day so, I shall do all of the cooling mods at once. I'm glad I basically crawl off in first at junctions etc and give the car time to get it together before booting it in second! I've been considering taking the waterpump out of the loop on my MR2 and replacing it with a temp actuated in-line pump. Would this be of use? That way you could also put the thermostat on the other side of the loop if that would help. It could also increase efficiency as it wouldn't always have to be one. Downsides - having the pump still in place (although the innards could be gutted). Edited by anonymous-user on Wednesday 10th August 21:19

Rockster said: Can't agree with everything you say. That low temp t-stat may not be the cure all you think it is. Tests have shown that as the engine temp goes down wear increases and fuel consumption increases. Here are some numbers: Temp Wear (cylinder) Fuel Consumption (GPH) 70F 0.008" 3.8 120F 0.002" 3.5 155F 0.001" 3.2 180F 0.0005" 2.9 210F 0.0003" 2.8 Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine. Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat. Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are precision cast into the head) are used which carry coolant from a larger passage to an adjacent but smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area (generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling. Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts. Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown. The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place. The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface. The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets. Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides. Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches. The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up. My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system. Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring. If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further. I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory. In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened. There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them. Sincerely, Rockster. I dont doubt your findings and content of your post,however I dont understand how you can can state the bore scoring doesnt apply,I can state it does Ive seen the metal and spoke to the owners on several occasions ,its beyond doubt these engines are (just to mention one know issue!) thermally weak I agree with Baz entirley remember he has a proven repair method and has an increasing pool of cases to refer to and monitor future issues. G Edited by Gary11 on Wednesday 10th August 21:38

Rockster said: Can't agree with everything you say. That low temp t-stat may not be the cure all you think it is. Tests have shown that as the engine temp goes down wear increases and fuel consumption increases. Here are some numbers: Temp Wear (cylinder) Fuel Consumption (GPH) 70F 0.008" 3.8 120F 0.002" 3.5 155F 0.001" 3.2 180F 0.0005" 2.9 210F 0.0003" 2.8 Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine. Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat. Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are precision cast into the head) are used which carry coolant from a larger passage to an adjacent but smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area (generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling. Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts. Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown. The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place. The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface. The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets. Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides. Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches. The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up. My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system. Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring. If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further. I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory. In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened. There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them. Sincerely, Rockster. Rockster, what you say is interesting and informative, but Baz is probably the world's foremost authority on these problems. He dismantles two or three scored and seized engines a week. He's got twenty guys working for him and large engine building rooms and machine shops remanufacturing and fabricating parts for these cars with ten ramps constantly on the go. They have several test cars driving around that they own and they have have been in the business for more than 30 years. People send their cars to Hartech from all over Europe and even some engines from the US. I'll go with what Barry says and I probably will have a low temperature thermostat fitted next time my car's in.

Hi Rockster, sorry I don't know your background but you have managed to put together a load of scientific facts that are basically right and then allowed the conclusion to be the opposite of both common and technical sense and practical experience. I explained exactly under what circumstances a stop start could occur (you didn't read it all did you?) and even explained why they are OK in racing conditions - so please don't muddy the waters by suggesting otherwise. What test is it that shows that oil is better at higher temperatures - everyone knows it degrades, is thinner and doesn't do its job as well when engines run too hot - that's why they suffer crankshaft and bore failures when the engines overheat and not when everything is nice and cool. You correctly confirm what I said that the coolant is going more slowly through the engine - can you not manage to work out that this must mean that it picks up more temperature than if it was going faster and therefore the temperature rise is greater (which is my point). if therefore the thermostat is set higher to start with AND the coolant is going slowly - the output temperature must be much higher and therefore so must the top of the bank 2 cylinder wall. Out tests showed that the coolant boils under pressure at about 25 to 30 degrees above atmospheric boiling point - but this is anyway not really relevant because if fan speed is higher this cools the coolant in the system more and therefore lowers the entry temperature to the engine through the thermostat. It is impossible to argue against the fact that if the inlet temperature is controlled by a thermostat - AND the amount of cooling to drop the coolant to that temperature (which it does as it is controlled by the coolant flow through the thermostat) then the outlet temperature from the engine simply must be higher. Our tests also showed that although it boils at a higher temperature it starts bubbling much sooner at lower temperatures - largely because of localised heat. Now lets ask another practical question - what do you do when your baked beans start bubbling in the pan - stir it, what do you do is heating milk starts to boil - stir it, there is no doubt that the slower the coolant speed across the surface the more it is likely to bubble. This is exactly what will happen when you stop for a short while and the engine slows down (and coolant pump) - there can be no argument to support the idea that just then the coolant speeds up - it obviously does not - hence bubbling more likely. You are also ignoring the fact that the overall temperature of the coolant is the result of it mixing back together from the head and the block - without doing the tests we did - you would not know what temperature the coolant from the block or head is before it mixes back together - I do - and what happens when we stop and start and drive fast etc - because we have tested just that with two cars witted with multiple temperature sensors in the engine and recording on different gauges - Have you done this? Once a piston has scored it no longer produces the same compression pressure before ignition and therefore runs much cooler - hence the oil temperature at the surface of the piston to cylinder wall interface is actually lower and the rings have less to do. Your comments that scoring just doesn't actually happen makes me wonder if you are working for Porsche under instruction to mix a load of technical rights with a load of nonsense conclusions to dilute the truth from being established. You seem to be living in a theoretical dream world in which you can persuade yourself that reality doesn't exist if your technical knowledge suggests to you it is impossible - but without practical experience and tests your conclusions are anyway totally flawed. Your posting seems to me to be from an academic with little practical experience and it is only that practical hands on work combined with technical knowledge that enables engineers to work out how they fit together and what actually happens inside the engine. Your last sentence is in all honesty disgraceful and I hope you are never confronted by the hundreds of owners faced with a financial disaster because they expected a Porsche to be better engineered than it obviously is - or for the manufacturers to do something to help them when faced with an obvious technical design shortcoming. I suppose at least you have managed to manipulate me to spending more time defending my advice than providing more (perhaps that was the aim and I fell for it) so at risk of allowing more similar nonsense to be posted and the resulting confusion from limiting the public's understanding - I am going to ignore your further posts and concentrate on advising those that can see through these and similar posts (and I am grateful to those supporting me with similar common sense practical points and experiences that prove that these engines have a bore scoring problem). I am still not sure why anyone would be motivated to discredit advice intended to help avoid damage - that can do no harm whatsoever to the car and could only help - unless there are more sinister motives - or they are the rantings of someone who has no practical experience and cannot bear to see someone else appearing to know the score and hold a place on the internet as an expert. I find it very sad that someone so obviously knowledgeable can spend so long discrediting someone with proven knowledge, experience and who is fully technically qualified, who has out-designed the might of the Japanese motorcycle industry and who clearly has resolved many of the existing problems and is simply offering some advice that might help. Presumably you prefer people to thrash their cars immediately after being forced to sit stationary for a while (because you think that could not cause scoring) rather than consider that there might be some good reasoning in my advice (combined with actual practical road tests and temperature readings) and therefore - as no harm could possibly be dome by my suggestions - just keep out of it. Baz

Rockster I appreciate your response but I'm with Baz. Unless you can prove your technical theories, having actually gotten your hands dirty and having had Baz's experience with these engines then I'm sorry I believe you are a Porsche Head Office Stooly. You always seem to oppose what Baz has to say. Baz food for thought eh ?.

Not sure why anyone would want to argue the toss against Baz, no one can possibly know more about the problems these engines suffer from. What has he got to gain by giving this advice. If everyone listens to Baz he will lose out on business as there will be less scored cylinders. This shows that he is genuinely interested in helping us. Lets face it, if our car is out of Porsche warranty and suffers an engine problem who are we going to trust to rebuild it???

I am in no way technically experienced with engine problems and am not in the profession, can I ask a question as a person from a basic viewpoint. With the water cooled rear engined porsches, what effect does the radiators being far away from the engines have? I assume they are at the front? also do the 997 engines suffer from the same problems? are they a revision on the 996 engine or a new design, if it is a revision and it doesn't have the same issues, what have porsche changed?

I'm not sure Baz has that much to defend here, I'm for one with him. But I can't get my head around the metal to metal contact of the bore & liner, I always believed that it was the oils job to stop it, hence my earlier post, that or 'Magnetec' has brainwashed me. Cheers.

hartech said: It is therefore clear that when the scoring occurs – one side of the piston is sufficiently cool to lubricate the piston/bore face and support the piston whereas the other side has become excessively hot and the oil film cannot support the loads applied – which result in metal to metal contact – overheating of the surface and scoring the bores and piston on one side only. This makes sense. The oil is shearing to 'nothing' under excessive heat in a specific area of the bore. So it is logical to look at the nature of cooling in that area, which is evidently problematic by design. If I had a 997 M97 I'd be running higher temp oil, and driving sympathetically as a precaution. BMW had very similar issues with their M motors and now the manufacturer insists on 10w60. It is odd that Porsche are seemingly silent - difficult for them to admit their failing I would guess. I wonder how they dealt with the myriad of teething problems with the air-cooled engine that took decades to perfect? And is Mobil1 0w40 what it used to be.. I wonder.

anonymous said: [redacted] It is quite possible. An efficient cooling system should be thermally loading the coolant media as high as possible, whilst reserving some capacity for use during times of high demand. The overhead capacity is an estimation made by the engineering team, having considered all the analysis available to them. Unfortunately, one of the first things you learn as a real world engineer designing complex machines is that all the tools you use (including actual test) are only an approximation of the real world. Some of the tools, methods, graphs, software etc are more of an approximation than others. Fluid Dynamics, along with FEA are, perhaps most susceptible to providing results that could be complete and utter tosh. And that's with todays technology. When were these engines designed? 1996? Thats an ice age ago in computing power and software capability. Of course, the key to useable results is to have a user that can apply his/her engineering bulls t filter to computer output to check whether the output is trash or not. This goes for bolted joints, to the flexure of airliner wings, to the airflow over those wings, to the internal flow of coolant in an engine. With the coolant system, an immediate and high demand will transfer heat through the cylinder walls fast (because the metal is already at a high average temperature, is thin, and transmits heat fast anyway) and move into the coolant adjacent to the cylinder walls, then it will have to propagate through the coolant media itself. I think it reasonable to say that the coolant media will only work under a certain temperature range for a given system pressure, and that range is far below that of the temperatures inside the cylinder during ignition (which I assume are highest for a max torque condition). The extra instantaneous heat load will, for a short time, exceed the thermal capacity of coolant local to the cylinder wall. The coolant at or near the cylinder wall will be slower (actually pretty much zero as it is the natural boundary layer) than the 'free stream' coolant flow within the engine, which itself, will be slower than the coolant flow around the rest of the cooling system. The actual time of occurence for these very high temp situations may only be relatively small, but, the overhead capacity of the coolant may only be 1 or 2 degrees local to the cylinder wall, so the cylinder walls would only need to transfer a small percent of the gas temp to cause trouble for the coolant. The real killer comes when the coolant adjacent to the cylinder wall bubbles up and effectively forms an air gap around the cylinder. Air is an excellent insulator, leading to heat being retained within the cylinder walls. As I understand it, the cylinder will then expand - which means the outer wall will move away from the centre of the cylinder, but the inner wall will move towards the centre of the cylinder, even if by a tiny amount. This can all go on within the engine and the operator may never see it because the coolant system has volume, and the extra heat will take time to propogate through the system. The 'overheated' coolant volume may only be a very small proportion of the total system volume so the average temperature rise when the 'overheated' coolant is finally thoroughly distributed through the system will be small. Yes, the coolant is moving, but it still takes time, and that time period is longer (probably much longer) than the high temp ignition period. On a 'global' scale, there isn't much to see, but on a 'local' scale you had a short term overheat condition. In terms of driving conditions, I can see when I have to do stop-start town/traffic driving, or nipping from roundabout to roundabout that my temperature gauge creeps up. As we now know, this gauge isn't providing us with the max temp in the system, so coolant temps will be even higher in some places. It seems the effective way to reduce those temps is to get the waterpump speed up and increase radiator air flow. You've got to get the car to speed carefully and drive it faster! I wonder whether this might be a case of lagging the engine (say accelerating from 25mph in 6th) just as much as frequent low road speed speed/high rev situations because the high revs would at least have the water pump working faster. I looked for a heat transfer example that might be applicable here so we could see just how fast energy is transferred from a hot gas, though a hot wall, to a coolant media, but it gets complex quick just for simple overall heat transfer coefficients. I'll keep looking.

I don't think I follow you on that one cmoose? I don't have need for this in aerostructures, so I had to go and look it up again. I don't think this link agrees with you? http://www.brighthub.com/engineering/mechanical/ar...

Only time for quick comment: the very prestigious US Porsche expert, LN Engineering are also keen to support use of the low temp thermostat, like Baz. Check out their site.....

Although I could get into a lengthy discussion about cooling and heat transfer etc I am sorry but I don't see the relevance. The only things we can change with these cars without stripping and rebuilding them (and even then we cannot change the material or much of the design) is the temperature of the coolant sitting next to the cylinder wall and the speed that it circulates. There must be no one who really thinks that slowing it down is going to make the surface between the piston and the cylinder wall cooler and no one who thinks that if it is hotter when it goes into the engine it will somehow cool the cylinders down more than if it were cooler. So lets confine our thoughts to these simple but totally relevant issues and accept that anything that reduces the initial temperature of the coolant going into the engine will lower the temperature at the cylinder wall and as the thermostat is on the way in and controls the in going temperature by adjusting the flow rate - the only way to get it to enter cooler is to run a lower temperature thermostat. Secondly, there is surely no one that thinks that after driving fast and suddenly stopping - the engine internals suddenly cool by themselves - I think everyone realises they see a rise - so increasing engine revs while driving off again must help speed up circulation to the radiators and back to the engine = quicker cooling while increasing revs provide more oil spray to cool the piston and crankshaft splash to lubricate the cylinder walls (all with oil that has gone through the oil cooler so is cooler than before when it sat inside the engine). Finally the scoring only takes place when one side (the thrust side) of the piston loses the oil film strength keeping it away from the cylinder wall. Is there anyone that thinks opening the throttle full open somehow provides less thrust force on that very face. That being the case, using a lower temperature thermostat and/or not giving the engine full throttle immediately after an enforced rest and keeping the revs up a bit as you drive off - can only help. All other thoughts - while interesting theoretically and no doubt interesting to some - have no bearing on what owners can practically do to help reduce the incidences of cylinder scoring - which is what I opened the posting about and perhaps are more at home in a new subject about the theory of heat transfer. Baz

Here is a bit of text from Wikipedia with some relevant content reinforcing the Hartech analysis. Baz can you help me understand, is the thrust face in question ie bank 2, the upper side of the right of the engine as you look at the rear? [edit]Coolant and heat transfer agent The major use of ethylene glycol is as a medium for convective heat transfer in, for example, automobiles and liquid cooled computers. Ethylene glycol is also commonly used in chilled water air conditioning systems that place either the chiller or air handlers outside, or systems that must cool below the freezing temperature of water. In geothermal heating/cooling systems, ethylene glycol is the fluid that transports heat through the use of a geothermal heat pump. The ethylene glycol either gains energy from the source (lake, ocean, water well) or dissipates heat to the source, depending if the system is being used for heating or cooling. Pure ethylene glycol has a specific heat capacity about one half that of water. So, while providing freeze protection and an increased boiling point, ethylene glycol lowers the specific heat capacity of water mixtures relative to pure water. A 50/50 mix by mass has a specific heat capacity of about 0.75 BTU/lb F, thus requiring increased flow rates in same system comparisons with water. Additionally, the increase in boiling point over pure water inhibits nucleate boiling on heat transfer surfaces thus reducing heat transfer efficiency in some cases, such as gasoline engine cylinder walls. Therefore, pure ethylene glycol should not be used as an engine coolant in most cases.

Do you have a picture of the coolant pump in question? Particularly of the blades/vanes side of the pump?

anonymous said: [redacted] That is true - and makes total sense, which is what I took from the page. Anyhow - low temp thermostat it is!

More reading on the low-temp thermostat (interesting comments regarding DFI and GT/TT engines): http://www.lnengineering.com/lowtemperaturethermos...

anonymous said: [redacted] I think we all agree this would be over the top, so it is a good thing Baz didn't say this. What he did say was: hartech said: Your last sentence is in all honesty disgraceful referring to this: Rockster said: There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them. Since the evidence suggests this can cause scoring I find it hard not to agree with Baz here.

Whilst I am not an automotive engineer I am a trained scientist and professional engineer in a different discipline. Baz has put forward a very plausible hypothesis to my mind, some of the negative comments with regards to things such as journalistic testing of vehicles beggars belief. Yeah right you can just expect to jump in and drive the car flat out away from the lights each and every time in any conditions and never expect a failure. Its hard to take comments like that even remotely seriously.

OlberJ said: Do you have a picture of the coolant pump in question? Particularly of the blades/vanes side of the pump? Reason i ask, have had problems before pumping coolant round a similar length system when a big engine is involved. We found the impeller blades of certain aftermarket pumps were not up to the job. If you can find/develop a better pump you may find that solves the stagnant coolant issue.

Thanks for the info Baz, spot on as always. While I cannot explain what was going through Porsche engineers minds when they put the thermostat on the return side on the engine. how easy is it to modify the system to put the thermostat onto the correct side? Also some months ago there was a thread where we discussed putting a smaller pulley onto the water pump - for the same reason, to speed up coolant flow at idle to stop boiling, have you had any thoughts about modified pulleys etc?

anonymous said: [redacted] Oh come on you must do better....anyone with ANY race or tunning/engine building skills knows after a period of hot running (either stationary in traffic on a hot day or after a high speed run) if you were to turn off the car the temp inside the engine continues to rise for a time hence with tuned turbo engines they sometimes have turbo timers ect thats just known basics,I dont think your qualified to speak on the same page as Baz,both as a pun and a fact!

anonymous said: [redacted] Oh ok "Regardless of the scenario" you simply cant be serious? G

Gary11 said: Oh ok "Regardless of the scenario" you simply cant be serious? G "I don't think five seconds of revving off the line is enough to conduct heat through the metal and in turn overheat the cooling system" We were discussing potitial causes of hot spots not overheating the cooling system in the normal sense,the basis of this (I think) is its normaly similar bore pick up on similar pistons with piston material deposited on bores. Again (I may be wrong) based around mechanical "inneficientcies" present in the design and sometimes poor construction by the manufacturer? Baz in another thread has measured the realtime engine temp being a lot hotter than the temp gauge. Edited by Gary11 on Sunday 14th August 13:23

I have measured on a dyno what happens when an engine is about to seize and then seizes by changing a parameter suddenly (mixture - coolant flow etc) It takes about 3-4 seconds from starting to overheat to the piston dramatically overheating and causing seizures. Whatever people theorise about that is a fact I have checked. Now on one forum someone had exactly the failure I suggested immediately after that stop and then flat out start scenario. Bubbles can appear very quickly and if bubbles appear at the cylinder wall the subsequent cooling affect in that small area is effectively zero. If 996 3.4's are OK but cayman S, 996 3.6 and 997 3.6 and 3.8 models fail we have to ask ourselves what are the differences. General design - no, piston material and surface finish - no, cylinder bore material or thickness - no, general cooling design - no, more force on the piston face at low speed full throttle driving - yes, higher coolant temperature inside the cylinder block - yes. Ask yourselves what link there could possibly be between higher piston face forces and temperatures and failures - it can only be the oil film going beyond some safe limit - what is different - the temperature and pressure. Nothing else in this scenario really matters - as many others have said if you turbo charge a standard engine you can get the same problem for which a period of revs without load is usually a suitable solution. 996 3.4's will do this scoring IF there is something wrong with the coolant flow or the coolant pressure going low (due to radiator leaks or pressure cap or expansion tank cracks or leaks - does this give us a clue - I would have thought so. Why so many people have to argue about a simple suggestion to help protect engines (that is actually perfectly good practice anyway) I don't know. At every step I supported reasoning with several different simple physical or technical facts about engines and cooling - there was nothing contradictory about it. Yes the top of the RH bank 2 is the thrust face and is hotter because the coolant enters at the bottom of both banks and the bank 1 thrust face is on that bottom. Again simple common sense links the failures being on bank 2 to this simple observation and logical technical link. Although (as someone somewhere stated) the coolant is travelling slower this also means it picks up a greater proportion of the heat - so bank 2 top will be hotter than bank 1 top. What is it about linking the thrust face being on the hot side of bank 2, the temperatures being higher than the previous almost identical engines that were OK and the thrust face forces being higher - that is difficult to follow and although plenty say I am wrong - where is their similar logical progressive link through several factors that I have measured and proven that they come up with as a plausable explanation for the failures - or is it simply - like some people say about the wartime horrors - that they simply didn't happen. Heads well in the sand, bums in the air - frankly some deserve to be kicked. This is not just a question of opinion that we all have a right to express - it is a fact that a lot are scoring bores - there is no opinion about that. If one person analyses factors involved and others dissagree - where are their alternatives that I can contradict - or is it just impossible for some people to just say - that's interesting - thanks. Amongst critics there are those that state the thermostat is on exit, that the hotter the engine is the better the oil protects it, it is gravity that causes the problem etc etc - well intentioned may be but totally off the track and simply adding confusion to those not sure about such issues. To all those kind and sensible people who have supported me on this a big thanks and appreciation. I might well not have it all right but why try and stop people from simply taking it a bit easier for a short while when leaving a stationary period - when there is a good case made out to suggest it might help - when in so doing it may well damage their engines? Baz

Baz I am grateful that you share your experiences and observations here, particularly on this very matter as, when my car is returned from its engine rebuild (due to suffering from scored bores) - hopefully this coming week, it's very useful to read any tips and pointers on avoiding it recurring.

Baz, just a side question if you don't mind - and not especially related to the flat 6 engines. Under full throttle, what sort of figure should the coolant temp not exceed on outer cylinder walls? As far as I know coolant temp varies between 80°C and 100°C under "normal" operating conditions, but I'm wondering what is usually the highest acceptable temp differential between the radiator and outer cylinders walls?

anonymous said: [redacted] Im so glad Baz stepped in! I can see NO help or function to the content of any of your posts questioning helpfull ideas made by someone who does this as a freebie (posting on here) cynicaly an engine rebuilder could advocate WOT at all times. I have spoken with many owners looked at mamy damaged engines and therefore feel more comfotable knowing why a particular engine is prone to fail and the repair proccess thereon. Im sure the temp monitoring was a bit more sophisticated than the cars own gauge! Its is reasurring as an owner to know there is a modification rather than like for like replacement of a flawed part. That is the purpose of (I hope Im right)Bazs informative posts IE a functioning PH forum. What use is your reply to anyone? and what "hands on" experiance have you to qualify your reply chap?

C'mon guys... Whilst I'm here... would there be any use, even if there's room, to add some kind of heat-sink block to the external (obviously) cylinder block wall? My uneducated guess would be that it must wick some heat away from the block?

ISTR this is certainly not a new problem for Porsche either. Baz can expand on the details but ISTR way back on the 944 S2 they could seize up very quickly if allowed to overheat and thus score the bores, although I always thought the tight piston to cylinder wall gap on that engine was part of the problem. More recently Baz had spotted this was also due to the HG deteriating on what are now mostly very old cars and allowing a coolant flow path effectively allowing one part of the block to overheat. Certainly not unique to Porsche either, I had a cylinder head crack on another car due to a hotspot most likely caused by an air trap in the coolant.

Wow that is some back tracking. You said you didn't believe a few seconds of power could heat up the metal enough to damage an engine yet Baz then said from his own testing an engine will fail after 3 to 4 seconds. Yes its fine to question the things those in the business say on here but at no point have you offered a counter argument based on either a credible analysis or experience.

Plus I know from first hand experience how head temperatures shoot up when an engine is stopped - I used to run an MG midget with a capillary thermometer (manual - not electric), very illuminating to see what happens when the coolant stops moving!! Worth bearing in mind that the difference between water boiling or not at 110C (pressurised water) is only a change of pressure or energy, and once it's boiled (on a quick traffic light getaway) 300BHP/6 = 50BHP are heating a cylinder wall without cooling. That's much more energy than a blowtorch. That they fail is un-surprising, and the fixes are obvious: 1) Reduce water temperature to prevent boiling 2) Increase flow rate to get heat away quicker 3) Reduce heat generated (power) So keeping some revs at the lights will help, as will a slower getaway (2 + 3). I still can't figure why Porsche would give us a dud temperature gauge and combine it with a thermostat on the return - it's just insane.

My suggestion is the engine is running too lean, this a guaranteed way to generate heat in such a short space of time. Next to me sat on my desk is a melted Toyota piston, but only one side (inlet side) & only the crown lip which led to bore scoring & failure. Caused by lean running in idle conditions. My bet is some dodgy mapping somewhere near idle lift off etc that leads to a lean/det related failure.

sportsandclassic said: I for one think for a relatively small outfit all things considered are doing a fantastic job ! I don't know of anyone more knowledgable than you in this field. Mike This graemel said: Excellent post Baz. Never let anyone on PH get you down. You keep doing your thing mate, cheers Graeme This DiscoColin said: Please don't be so melodramatic Baz - many of us out here really do enjoy a lengthy technical post in terms that we can understand This too. anonymous said: [redacted] and this. It is my belief that there is nobody that knows more than Baz about these engines, and I am another one who greatly appreciates the time he takes to post his findings and his thoughts/theories (Such is my belief in him/his operation that I became a ‘Maintenance scheme’ customer even though his premises is over 300 miles away). I’m sure, however, he will be the first to admit he doesn’t know everything there is to know, and he still spends a lot of his time investigation and trialling things and there is still scope for technical discussion. Baz – don’t take any ‘queries’ on your wisdom as any form of personal attack. Just use your considerable experience/knowledge to rebuff/debate their points as appropriate.

This is a very interesting thread and I'm grateful to the various contributors for their explanation of the technical goings on inside the engine when things get hot. What I can't quite get my head around is that Porsche designed the engine with the thermostat on the wrong side of the rads, there MUST be a logical explanation for this ... surely !! Try and keep the bickering to a minimum guys, it's detracting from the thread.

Look chaps - I don't have a lot of time for all this - I spend hours trying to solve problems created by a much bigger and wealthier organisation than mine and then more time trying to advise people what I find out - only to have - in some cases - very ill informed questioning requiring me (they think) to spend even more time explaining why their opinion may just be out of line - or completely wrong - or indeed exactly right. I honestly don't have the time and when the questions clearly demonstrate very little knowledge of the engine or little practical experience - or - are just put there to glorify someone else's ego - I do get tired of being expected to patiently advise all and sundry - yes I should be more patient - yes I should spend more time just advising people that know very very little anyway - yes I should be less touchy - but I am also trying to find out much more advanced issues, design solutions, develop tests and answers and run a busy business - one of the few doing anything at all about a serious design error. So - I am sorry I am such a grumpy old man - sorry I think I know more than most people - but honestly - if most just took on board what I offer and resisted arguing all the time (mostly with frankly very poor technical comment or completely inaccurate points) - I could get time to offer a lot more advice that might be more useful to readers than fighting silly arguments and answering questions raised by people for whom the answer will not help them, not change their mind but just take my time. Now after that genuine apology - the S2 piston has little taper and the cylinder bore area (in common with the later liquid cooled engines) has relatively shallow coolant block depth. It does run tight and can seize at the top - but ALL these scored bores occur down the bottom of the piston - on the thrust side - they have nothing to do with ignition or fuelling - and they are not a full seizure - only on one side. This means that while the piston is pushing hard against the thrust side (like the piston had expanded too much like most seizures) the other side is not hard against the bore and is lubricated perfectly OK. The thrust load is not all that high but the temperature is and therefore the oil is extremely thin and watery - poor support = scoring. The thicker the cylinder wall the less heat can be transferred through it quickly - but the problem is really one of bubbles in my opinion. If the cylinder was upright (or almost upright) bubbles naturally rise away from the hot spot and new coolant rushes in its place - but in a horizontal engine with slow coolant flow - it is trapped. The outside of the block is almost exactly the same size as the original 2.5 Boxster and has been increased through the Boxster S, 3.4 and 3.8 engines until there is very little clearance between the outer cylinder wall and the block - so very little distance for bubbles to float away and be replaced by coolant. This also restricts the thermal current that allows hotter coolant to swap places with cooler coolant in the same area of the block in engines with more coolant space. Furthermore the block height (from centre of crank to cylinder head) is exactly the same in all these engines despite two increases in stroke length. The consequence of this is shorter rods and/or (depending on the engine) moving the gudgeon pin position upwards in the piston - both adding load to the piston skirt (from identical cylinder pressure on a longer block height). It just seems to me that in the pursuit of more power and torque (through bigger bores and strokes and introducing variable valve lift) the engines have been pushed closer to a safe working limit while little or nothing was done to improve basic cooling etc to compensate - in fact in some areas it appears to have been made worse. It is therefore perfectly expected that a higher number will suffer failures (and entirely common with many other previously reliable engines that were basically bored out or stroked for extra performance without the benefit of complete redesign compensation). Obviously a small engine increased in capacity - makes a very fast car but reliability can suffer. I would challenge anyone to make out a case that by offering both the low temperature thermostat (at a lower price than from the USA) and advice on how I think owners maybe able to avoid scored bores - I can be trying to increase my businesses profitability. It should be obvious to an idiot that I would be better off keeping quiet and just posting about their shortcomings and fixing more failures. If my motivation is clearly not commercial (in fact goes against our income potential) and I have backed up my advice with a list of technical explanations that hold up - why so many arguments and why do so many people think I should then have to explain in detail the answers to all their questions when often they are so far out from reality I would need to spend hours just teaching those same people about engineering etc before they could understand the answer. Of course I will not always be right and of course it is interesting to read about other suggestions when they are realistic and relate to the actual engine and genuine engineering principles - but they are few and far between and I just don't have time to explain to everyone in detail the why's and wherefores of every post I submit - sorry guys! On a purely personal note - I hate having to act so arrogantly - those that know me well know that I always discuss ideas with staff and encourage comment and disagreement - and I would prefer to just be known for my knowledge and helpful advice - but it becomes difficult to find time to respond to the level of feedback on the Internet and at times I simply have to resort to blunt facts that make me appear extremely bog headed (I know). I hate it but seem trapped by time constraints into that somewhat inaccurate image. It is difficult to get away from that situation when a person does know their stuff. Give us a break for a while please. Baz

Globs said: Plus I know from first hand experience how head temperatures shoot up when an engine is stopped - I used to run an MG midget with a capillary thermometer (manual - not electric), very illuminating to see what happens when the coolant stops moving!! Worth bearing in mind that the difference between water boiling or not at 110C (pressurised water) is only a change of pressure or energy, and once it's boiled (on a quick traffic light getaway) 300BHP/6 = 50BHP are heating a cylinder wall without cooling. That's much more energy than a blowtorch. That they fail is un-surprising, and the fixes are obvious: 1) Reduce water temperature to prevent boiling 2) Increase flow rate to get heat away quicker 3) Reduce heat generated (power) So keeping some revs at the lights will help, as will a slower getaway (2 + 3). I still can't figure why Porsche would give us a dud temperature gauge and combine it with a thermostat on the return - it's just insane. Are you sure about keeping some revs at the lights? Will that help with no airflow through the radiators? So far my 997 has been OK but it is warmed up properly, rarely taken even close to max revs or hammered away from light etc (why would one do that?) and has the oil changed every 12 months/4000 mile maximum but I am convinced by Baz's theory. After all it just has to help doesn't it? Where do I go to get one of these low temp stats properly fitted?

DSM2 said: Are you sure about keeping some revs at the lights? Will that help with no airflow through the radiators? You want to keep the coolant flowing around getting heat out of the hot-spots, the radiators will look after themselves, especially if they have fans (which they must have or you'd overheat in traffic). DSM2 said: Where do I go to get one of these low temp stats properly fitted? From Hartech Removing a few degrees from your engine can only help move you away from the boiling point - a very wise move (although it may cut down on the number of engines Baz has to rebuild, but I suspect that's not going to be an issue with these!).

This thread just highlights what a joke Porsche as a car manufactuer now are -seriously, holding revs at lights, don't accelerate too hard away from a standstill etc etc. Pay many tens of thousands for a perfomance car and then you drive around doing all that - screw that - after my 996 is moved on I'm not coming back to the Porsche brand...if I want all that hassle I'd buy a Ferrari.

Baz and I bickered a bit on the 996-997 wet-sump reliability thread in the early days - because of one or two differences in our interpretations of statistics and our sampling methods (long story, not worth digging up). The thread almost deteriorated too far, so I started another to use as a lightning conductor. That worked (it got locked, but it was a good dump for the inevitable vitriol that came from a few sycophants). Baz and I always agreed on the issues with these engines (based on different experiences) but our disagreements were magnified by two things: 1. The sometimes curt responses we gave to each other or others as we responded whilst doing something else (or just because......); 2. The tendency of some sycophants on here to suggest questioning Baz is sacrilege. This is another very useful thread which I hope will become a sticky. It hasn't deteriorated as far as the current sticky did at one time - because people now accept and know there are serious issues. So folks, yes please do keep the questions coming, but please add a little extra diplomacy because we're all doing this on the run and forget a phrase can be misunderstood! Funnily enough, I scoffed publicly on here at a comment Baz made (years ago on the 996-997 wet-sump reliability thread) about the driving style of 996s contributing to the problem. On reflection (much later), I realised that I scoffed because I didn't drive any of my cars that way but my scoffing became less valid because I took care to notice lots of porkers (and some other cars) being driven as he described. It is still as he has stated on here - hot engines not cooled properly, and then setting off with high load from the lights, sometimes just for 100-200 metres only for the cycle to continue again! That could never be good for any engine, howsoever well cooled. He's right, of course. I don't need to see the inside of any engine to know never to do this. But I also never raise my revs at the traffic lights to maintain coolant flow. What I do do is take the long route whenever I can to ensure my oil temperature is falling rather than rising when I am parking up, and if it isn't, I'll go round a block or two swiftly to get airflow and the water pump going, coasting downhill if I can find a hill, to help drop the oil temp. The article by LN Engineering is really instructive and gives me some comfort thanks for the link! Like DSM2, I also change my engine oil frequently (usually half the recommended intervals - this I learnt ages ago and it is common practice in California and elsewhere). Never had an engine fail, usually got six figure miles out of them, and usually drove them in anger for sustained periods, but always let them cool properly before shutting them off. Thanks to all who have continued to maintain this thread with useful info, and to Baz for starting it. Baz, you have to accept that by pioneering this question/issue on here, you're liable to take a few (often unintended) arrows from those who will/must question some of this, even when they agree with you. Much as Tonikaram and I did when he started the 996 wet-sump reliability thread before you and I proved we agreed on it and had the title changed to the 996-997 etc, etc. Keep up the good work, folks. This is what makes this PH forum so valuable!

steve singh said: This thread just highlights what a joke Porsche as a car manufactuer now are -seriously, holding revs at lights, don't accelerate too hard away from a standstill etc etc. Pay many tens of thousands for a perfomance car and then you drive around doing all that - screw that - after my 996 is moved on I'm not coming back to the Porsche brand...if I want all that hassle I'd buy a Ferrari. Out of interest, and I mean no disrespect, but have you suffered an engine failure or are you just getting caught up in the hysteria? I'm very grateful to Baz and others for contributing here and making me better informed about where the flaws in the engines lie, but I have every intention of continuing the traffic light grand prix Hang on. On reflection, it's actually VERY rare that I use full throttle from a standstill - it's usually on aggressive overtakes... but either way I'm not going to change my behaviour and I still consider the 911 to be the only sensible choice for a daily driver sports car.

[redacted]

[quote=GT Glee] I wonder how they dealt with the myriad of teething problems with the air-cooled engine that took decades to perfect? Care to elaborate, Whatever these were? Still a monumental bottom end to rest on helped no doubt!

Gary11 said: GT Glee said: I wonder how they dealt with the myriad of teething problems with the air-cooled engine that took decades to perfect? Care to elaborate, Whatever these were? Still a monumental bottom end to rest on helped no doubt! I think the most frustrating issue is Porsche's ineptitude in fixing this. Allowing more cooling in the block, moving the thermostat to the outlet side, and putting a smaller pulley on the water pump would have cost them about £1 per car extra, tops. Then there's the IMS bearing - buying a non-shielded bearing solves that, job done. Instead we have to buy the faulty items, and drive it carefully with full mechanical sympathy everywhere and have the engines rebuilt when we don't or when it feels like letting go. Crazy. And this has been going on for years. As it is building a 'new engine plan' into each purchase has now become the norm, it's a testament as to how good the rest of the car is that they are still well worth buying!

Scelto said: steve singh said: This thread just highlights what a joke Porsche as a car manufactuer now are -seriously, holding revs at lights, don't accelerate too hard away from a standstill etc etc. Pay many tens of thousands for a perfomance car and then you drive around doing all that - screw that - after my 996 is moved on I'm not coming back to the Porsche brand...if I want all that hassle I'd buy a Ferrari. Out of interest, and I mean no disrespect, but have you suffered an engine failure or are you just getting caught up in the hysteria? My current 996 had a new engine from Porsche when it was owned by the previous keeper (at around 45k miles).

Baz, is the low temp thermostat something that can be installed by a reasonably competent DIYer? (2002 996) Is it within the part circled in yellow? Edited by matsmith on Monday 15th August 15:33

Globs said: I think the most frustrating issue is Porsche's ineptitude in fixing this. Allowing more cooling in the block, moving the thermostat to the outlet side, and putting a smaller pulley on the water pump would have cost them about £1 per car extra, tops. Then there's the IMS bearing - buying a non-shielded bearing solves that, job done. Instead we have to buy the faulty items, and drive it carefully with full mechanical sympathy everywhere and have the engines rebuilt when we don't or when it feels like letting go. Crazy. And this has been going on for years. As it is building a 'new engine plan' into each purchase has now become the norm, it's a testament as to how good the rest of the car is that they are still well worth buying! My assessment is that this is Porsche's business model. They benefit most from the faults (even as the marque devalues - which paradoxically helps the business model!).

bcnrml said: My assessment is that this is Porsche's business model. They benefit most from the faults (even as the marque devalues - which paradoxically helps the business model!). Could you explain this please?

R Soul said: bcnrml said: My assessment is that this is Porsche's business model. They benefit most from the faults (even as the marque devalues - which paradoxically helps the business model!). Could you explain this please? Something I suggested too. It works like this: 1) Your buyers who can afford to buy new, keep in OPC warranty, until they buy new again. 2) The other buyers would never buy new anyway, so why should they care. 3) Reliability of brand (image) is relative to Lambo/Fezza/Masser and has image from the past 4) QED bean counters decide perhaps it isn't such a bad thing after all, and stop anyone fixing the issues. Personally I think this carries over from VW, which for years now have been shockingly unreliable and a liability to own, but the PR image of solidity and German engineering replace the real mechanical quality. I think it's a false economy and will bite them, but obviously their directors disagree, viewing each quarter's profits more carefully than their cars. In fact the Cayenne shows me they have no interest in cars, despite the fact the sports cars remain most excellent to drive.

Gary11]T Glee said: I wonder how they dealt with the myriad of teething problems with the air-cooled engine that took decades to perfect? Care to elaborate, Whatever these were? Still a monumental bottom end to rest on helped no doubt! For example cylinder leaks of the 3.6 in the early 90's, which required new pistons and barrels. Hardly a minor fault and hardly an inexpensive one to remedy, thus my inquiry as to how Porsche handled this. Did they recall or bury their heads in the sand?

[quote=GT Glee] For example cylinder leaks of the 3.6 in the early 90's, which required new pistons and barrels. Hardly a minor fault and hardly an inexpensive one to remedy, thus my inquiry as to how Porsche handled this. Did they recall or bury their heads in the sand? I dont think its an endemic problem,and did not not affect every air cooled model it also didnt very often need new barrels and pistons and was mainly a 964 issue. It certainly hasnt hurt the values of 964 (once quite undesireable) now making more than 996 on a regular basis and enjoying a resurgance in popularity I cannot think of many blown engines ect ect. But take your point the 964 did have oil leak issues most are now sorted and did not need engine rebuilds. However it was nothing like this in volume or expense other than in principle and did not generate 50 page reliabilty threads! air cooled engines are tried tested and strong!

Globs said: I think the most frustrating issue is Porsche's ineptitude in fixing this. Allowing more cooling in the block, moving the thermostat to the outlet side, and putting a smaller pulley on the water pump would have cost them about £1 per car extra, tops. Then there's the IMS bearing - buying a non-shielded bearing solves that, job done. I know that £1 doesn't seem like much, and each owner (given the choice) would happily have paid £1 on top of the purchase price for a more robust engine, but from the manufacturers point of view, £1 per car is a huge amount when multiplied by the total production volume. Most OEM's are delighted if an engineer can find a cost-save of a few pence per car, never minds whole £'s.

Globs said: R Soul said: bcnrml said: My assessment is that this is Porsche's business model. They benefit most from the faults (even as the marque devalues - which paradoxically helps the business model!). Could you explain this please? Something I suggested too. It works like this: 1) Your buyers who can afford to buy new, keep in OPC warranty, until they buy new again. 2) The other buyers would never buy new anyway, so why should they care. 3) Reliability of brand (image) is relative to Lambo/Fezza/Masser and has image from the past 4) QED bean counters decide perhaps it isn't such a bad thing after all, and stop anyone fixing the issues. Personally I think this carries over from VW, which for years now have been shockingly unreliable and a liability to own, but the PR image of solidity and German engineering replace the real mechanical quality. I think it's a false economy and will bite them, but obviously their directors disagree, viewing each quarter's profits more carefully than their cars. In fact the Cayenne shows me they have no interest in cars, despite the fact the sports cars remain most excellent to drive. Item 1 above - Yes. Item 2 above - we broadly agree, but the definition of other buyers is key to the paradox I referred to. Let me expand further with a shorter version of my originally longer post. Faster depreciation (due to the reliability risk everyone knows about) = a greater perception of affordability, coupled with the German engineering (invisible and not so effective) cloak (I prefer charade myself.....). That means for the M96 and M97 engines, more new-to-Porsche ownership suckers buying at 2+ years old, all the way to 10+ years old. With the same problems (unless they have an Autofarm, Hartech and/or LN Engineering solution which will create an alternative market Porsche's not really interested in). Porsche needs those pesky M96 and M97 engined cars to die. Because the new DFi engine is the new emperor (see later). Extended warranty = insurance policy that ties you to a subscription (however relaxed that might be except for the big bucks engine scenario when the compliance standard focuses on pedantry). Porsche doesn't lose any money on this (small or large claims). The buyers collectively do (else the policy would have been withdrawn). Indeed, by going to a two-year model, they're getting their money upfront, making the model highly cash positive! Those cars run outside of the OPC network will succumb to component failures of all sorts, not just the dreaded engine failure modes. More money for Porsche, but if/when a catastrophic engine failure occurs, especially outside the network, a big bucks pay-day occurs using engine components that are similar to the originally "weak" (IMO - not humble either!) design. So the cycle continues..... Cynical me feels this is not a design weakness per se, but a design choice based on a reliability profile that feeds the Porsche corporate entity with cash and new subscribers. It is, in my view, an alternative version of the fact that the light bulb firms can make light bulbs that last far longer than they do. Which is why you have a two-year OEM warranty in the EU, the legal minimum required. Same as VW. And before the takeover Your Item 3 - agreed again. However, the benchmark is no longer those marques. Other (lesser, arguably better) marques are well within the envelope, but remember all those suckers moving from other sporty marques and seeking a Porsche for a few months or a year? That churn is really very important to Porsche's model. One recently came on here with a broken Cayman engine and an 11k bill (which he'll pay 1.2k towards). Porsche wins. Sure, others do too, but the beneficiary of the most costly bits is Porsche. Sorry to the three guys on that one thread with broken Cayman cars (no offence meant to you when I say suckers). In this model, the depreciation hit is almost solely the customer's - it has always been thus - and it feeds the affordability image and pulls in more suckers. The benefit of engine failures is entirely Porsche's - because they "look after" those within the subscription model and there are many (especially on here) who prefer to think they were unlucky. There are also many on here who buy into the same problem repeatedly because they've been "looked after" on something that really shouldn't be happening on this scale for any German engine manufacturer. OPCs? In my experience of a certain one owned by Porsche UK, during a morning test drive in London, the car was driven hard (not by me) by the driver. He was the first in that car - and I know it was not warmed up first. When I asked if this was okay (it isn't), he said they're designed to be able to take this. Ah, I thought. Remind me never to buy an ex-demo porker, or even a used one. Why would an OPC encourage the driving of these cars in a manner contrary to the message some of us (including and especially Baz) suggest is not acceptable? Just look how many people come on here and still don't know how important it is to run the cars in properly for the first 2-3k miles! Shouldn't the OPC tell them? Shouldn't Porsche (flashing light to warn of oil temp too low or too high)? Now as for the DFi, it fits this very model very well. So new suckers for the old subscription model. But I'll leave the DFi's essential contribution for another DFi focused thread. Sorry for the long post, but you did ask..... --- ETA this: This will only bite them hard if their sales in China fall sharply due to this problem. But they'll find a way to avoid this just as they did in the US with that market's four-year warranty! Edited by bcnrml on Monday 15th August 19:03

BCNRML, I doff my virtual cap to you sir!

matsmith said: Baz, is the low temp thermostat something that can be installed by a reasonably competent DIYer? (2002 996) Is it within the part circled in yellow? Edited by matsmith on Monday 15th August 15:33 Is it just me or was there a hover option for the 996 range ?

anonymous said: [redacted] So now you are suggesting 40-60% of Boxster engines fail or will do!

sportsandclassic said: matsmith said: Baz, is the low temp thermostat something that can be installed by a reasonably competent DIYer? (2002 996) Is it within the part circled in yellow? Edited by matsmith on Monday 15th August 15:33 Is it just me or was there a hover option for the 996 range ? Didn't spot that photo! Maybe a bit of DIY needed to whip out that thermostat and put an inline one into the outlet side..

matsmith said: Baz, is the low temp thermostat something that can be installed by a reasonably competent DIYer? (2002 996) Good write up on 911UK, see FAQ's in the 996 section, it doesn't look too difficult...

anonymous said: [redacted] With respect some of your theories have been proven wrong by some of us on here. Take the profit theory previously oft-spouted here. I've demonstrated (as have others party to the management accounts) that Porsche's profits were based on engineering of the financial kind, not of the mechanical. Their R&D investment was/is nothing special either. Components are shared with VWs and Mercedes, for instance. You can require your component suppliers to design to a defined timeline based on scenarios for use. Thus why are Porsche engines in the US warranted for only 50k miles (albeit over four years)? Why do radiators fail so often on these cars? As for your last paragraph, this is so flawed in statistical terms I know not where to start. But I'll end here: Just because a car is still listed as running doesn't mean you know how many have replacement or rebuilt engines it has had. I suggest (again respectfully) that you review the early-to-middle years of the 996 wet-sump reliability thread to explore the discussions on the statistics to which you refer. Finally, my theory isn't complicated at all. It is gloriously simple in design and execution. Porsche's management did something far more complex when they applied the financial engineering that led to the company's demise (that then came back to bite them, and may yet do again through litigation). Gary11, thank you. I doff my hat to you too. And with that, I'm leaving the debate.

bcnrml said: Why do radiators fail so often on these cars? That's a good question, and something I had wondered about. Any info?

Globs said: That's a good question, and something I had wondered about. Any info? Hi, They don't fail all the time, the main problem is debris left along the bottom of the radiator casing and just ferments. The fins along the bottom also get battered by the weather,stones etc. I think the turbo/c4s radiators are poor quality and porous. Normal 996/Boxster and gt3 radiators are all the same, these fail less than the turbo/c4s rads in my experience. Mike

Thanks for all the radiator info - esp. Mike, very informative. anonymous said: [redacted] Cmoose - do you have any explanation as to why Porsche ignores a serious design defect for many years? Especially one so easy for them to fix. I'm thinking there can only be two answers: a) They are incompetent or b) They chose to leave the problems there

Just a thought how about adopting an electric water pump that would run flat out regardless of engine speed. Something like this http://www.demon-tweeks.co.uk/Motorsport/Cooling_S... It could be a cheep way of keeping coolant speed up.

Matt Seabrook said: Just a thought how about adopting an electric water pump that would run flat out regardless of engine speed. Something like this http://www.demon-tweeks.co.uk/Motorsport/Cooling_S... It could be a cheep way of keeping coolant speed up. There could be mileage in these bits - although you are at £300 with that pump + controller - but in Porsche terms, not that much. The inline thermostat housing (http://www.summitracing.com/parts/MEZ-WN0071/) isn't massive money. Could be a very useful upgrade.

Globs, I'd like to add this to Mike's answer. The design is IMO flawed, probably because of the compromises required given the body shape, water cooling and emissions challenges. But even if you accept this positioning compromise (I do), why on earth do they fail so often, and why are they the only cars that seem to need so much preventative work on radiators? Why did Porsche prefer no extra protective grilles as offered elsewhere, and which are considered unacceptable under the extended warranty scenario? They allegedly said those extra protective grilles negatively affected cooling. Which suggests they know there is a cooling issue so significant the extra protective mesh would be unwelcome. So the rads get exposed to stuff that shortens their life. Which may also affect engine cooling efficiency, thereby exposing the engine further, something Hartech (and likely LN Engineering) have been working on? None of this is unconnected. Is it negligence? Or design laziness? And whichever it is, who benefits most? Definitely off now, but will pop by to read engineering updates, leaving the commercial stuff to others so inclined.

Hi Baz and forum, Just a question and I am no engineer by trade but more intrigued..... I thought that the liners were going oval on thrust side thus combustion gases were bypassing the piston rings and carbonising the oil down the piston skirt/ liner ? Surely this will cause a oil breakdown between the liner and piston area ? Correct me by all means we can all learn something everyday. Mike

sportsandclassic said: Hi, They don't fail all the time, the main problem is debris left along the bottom of the radiator casing and just ferments. The fins along the bottom also get battered by the weather,stones etc. I think the turbo/c4s radiators are poor quality and porous. Normal 996/Boxster and gt3 radiators are all the same, these fail less than the turbo/c4s rads in my experience. Mike +1 exactly the alloy seems cheap and poor quality,it would help a lot if they were anodised and a bespoke debris proof grillwere fitted,non restrictive obviously.

anonymous said: [redacted] Here we disagree, the failure rate is going to be almost 100% over a 20 year life, and no re-engineering was really needed to make the vital improvements. Just ordering a smaller diameter water pump pulley would have saved a lot of engines, changing the flow ratio between head and block is frankly trivial for them, moving the thermostat is a bit more difficult but not insurmountable. Then the IMS - ordering a bearing without covers. Also if you do not think they are doing this for the money, explain why Porsche are happy to build complete new engines, ship them over and have OPCs fit them and claim the money back, rather than fixing the fault. A fix like this in the field is _not_ a cheap option, it has significant costs. What is certain is that there were many Porsche engineers jumping up and down wanting to do this, having worked in industry there is _always_ someone who cares and wants to fix stuff.

I have tried the electronic controller on a Westfield and I am not keen. An old fashion wax stat works much better IMO. Edited to add they may have improved the controller now as it was about ten years ago I had one fitted. Edited by Matt Seabrook on Monday 15th August 22:13

Baz (et al) Would this be of use to some of your experiments? http://www.plxdevices.com/sensormodules.html (fluid temp device at bottom of page)

Gary11 said: ...it would help a lot if they were anodised and a bespoke debris proof grillwere fitted,non restrictive obviously. I'd buy some... whilst fitting that centre rad!

This is just how PH is getting, just pedantic comments for the sake of it.Who would write on such a subject after reading god knows how many threads and tales of woe that ..."Everyone I know who has a water cooled Porsche says theirs smokes and its nothing to worry about" Well your wrong...again....as usual. If true Im happy to remove it all really, I was only trying to help someone make a mistake potentialy costing them thousands of pounds....CMOOSE dont even bother replying....please. [footnote]Edited by Gary11 on Monday 29th August 13:51 Edited by Gary11 on Monday 29th August 13:53

anonymous said: [redacted] "Also, everyone I know who has one of these water cooled flat sixes says theirs can sometimes some a bit on start up, depending on how the car gas been used. Mine seems to do it if the previous outing was very brief." Sorry I tried to quote perhaps not as sympatheticaly as you would like! mustve been the typos,well we will leave it here no offence taken on my part as usual. Smoking is not "normal" on an M96/7,I just could perhaps understand a black and white disagreement but an innane "It doesnt always mean theres a problem" just seems pedantic and troly to me.After all the issues exist as we all know,surely any help spotting this is a plus?

anonymous said: [redacted] Ok thats fine Im refering to regular smoke on startup (theres a broken cayman thread refering to this) I just take the view that its something...a flag if you like to make you look and think rather than ignore beacause mostly its nothing to worry about.. plenty of times it is ,same as the rads they dont always leak just beacause they are old,sometimes the coolant systems over presurise the continuing expanding and contracting weakens the already poorly manufactured structure making them leak any evidence of this pressure damage is a warning to be heeded and looked into as is damage to exp tank and cap its cause and effect engineering basics TBH.When you change a head gasket for instance would you not look for the reason it failed rather than just changing it and handing it back as job done only to have it back a few days later with the blades fallen off of the water pump needing another head gasket? I dont profess to be an expert of bazs calibre but most of the problem cars I see exhibit 1 or 2 of these symtoms I just based my list on what I know and see rather than (as said before) on what I think,I hope I havent offended and havent meant to shout down a valid point intentionaly. I gauarantee out of ten M96/7 engines smoking on startup boroscope them 4 or 5 will have scored bores!

anonymous said: [redacted] He did only say "be wary of non-specialist rad changes" - I took this to mean check it was infact done properly, not avoid. As I do some DIY myself I feel able to qualify my work & justify to a buyer why it can be trusted - I think this is all he meant. If you found a car with a bill showing the work was done at e.g. kwikfit, I'd say that was at least cause to be a bit nervous and do some checks.

anonymous said: [redacted] "not really sure what you're getting at re the rads and making a buying decision" Ok Ok thats fine, I now 100% wish I hadnt replied ,if you think any previous potential overheating isnt an issue ,please you just enjoy your Boxster. Edited by Gary11 on Monday 29th August 19:35

[redacted]

I am always aware that there is more to learn and that I wish I knew more than I do - so I thought I ought to do some research into oil and lubricating engines - to see if any of it added any weight to the points I have made about ways to avoid pistona dn cylinder scoring. Most of what I read generally agreed with what I had posted - briefly that - viscosity varies riughly in a straight line with temperature (so if temperatures increase a higher viscosity oil would then work as well or the same as a lower viscosity one did when it was at lower temperatures), that increased bore clearances require higher viscosity oil (and we know that the open deck design allows increasing ovality and also increases deposits into the oil that reduce its capabilities and requires more frequent changes - when the models afftected have increased oil change mileages, etc etc (but not us as we still change oil on our Lifetime Maintenance Plan no longer than 12 months). We already have tested and proven that these engines run hotter than more traditionsl ones and that as radiators, pressure caps and expnasion boxes start to leak/age - they system pressure may reduce - lowering the boiling point etc. I have already mentioned that at low revs and low car speeds the coolant will get hotter (due to lower air flow in the radiators and lower coolant pump efficiency). But there was one significant issue I read about - that I didn't know before - but that has relevance (and supports my advice). That is that the lower the velocity the higher the viscosity needs to be. This also fits in with my motorcycle engineering experience in which large cylinder 4 strokes do tend to have a scoring problem at low revs but high torque (and hence piston to cylinder wall loading). When analysing the differences in the 3.6, 3.8 and 3.4 Cayman S engines - I mentioned that they produce more torque at low revs and that (in the 3.6 and 3.8) the con rods are shorter (so the piston face load against the cylinder wall - is higher). Following the engine oil/lubrication technology I researched - it seems that this should really coincide with a higher viscosity oil - but it has not (except in our case - where we recommend it). this all adds weight to my suggestion not to floor the car from a standstill - but to build up speed and load more gradually. Baz

Hi there Here is a question as there seems so much emphasis on engine cooling. The 997 C2S in standard form just has the two side radiators. The 997 C2S Tiptronic has the centre radiator for additional cooling. The 997 C2S X51 has the centre radiator for additional cooling. So as cooling seems very important and I agree, hence why I fitted the X51 radiator kit to my car and it has indeed lowered temperatures by a good 10c under load. To those who see these cars fail, have any X51 or Tiptronic cars failed? Or have all failures so far been cars without centre radiator?

hartech said: The problems discussed here relate to......"3.6, 3.8 and 3.4 Cayman S engines". Baz Does it also relate to the 987 S (3.4) engine ?

Yes, this engine started out as a 2.5 so any increase will make it more critical.

Its the A91 engine.........

Gibbo205 said: Hi there So as cooling seems very important and I agree, hence why I fitted the X51 radiator kit to my car and it has indeed lowered temperatures by a good 10c under load. How do you measure and see that temperature drop? What temperature does the car run at now, typically?

systech said: Does it also relate to the 987 S (3.4) engine ? The 3.4s engine is the Cayamn / Boxster 987 engine.

Hi Baz, Reading this topic did you get anywhere with the water pump upgrade suggestion? Thanks

Regarding the 987 3.4 engine - it too should be vulnerable but we can only judge on the numbers we see and so far very few. Perhaps some subtle selection of more careful drivers choosing that over a Cayman S and driving it accordingly less vigorously may explain that. Although we fitted 4 temperature sensors to 2 different engines in different places - to check out theories and results - it would take much more research to establish exactly what has been going on - using different models and with or without central radiators etc. We have already carried out far more research than any other Porsche business but the scale of the problems afflicting several different models and capacities is completely beyond our resources to address. Instead we have to use a combination of our test results, engineering good practice, the reliability the engines we have modified enjoy and the satisfaction of our customers to support together with a lot of good engineering judgement (of which long term readers of our buyers guide will note that we were first to explain all the causes of the problems - and that all the solutions we mentioned then were not only implemented but have been behind our superb reliability record ever since. I can tell you we are now regularly getting engines in for rebuild that have different designs of steel liners - that have failed. This not only supports our views (and clearly those of Porsche themselves who use exactly the same cylinder and coating as we do to rebuild our engines - in the GT2 and turbo engines) but it interestingly means that other businesses and owners are not going back to whowever provided those rebuilds (or they have refused to honour any warranty on their steel liner'd engines). There are a lot of others getting in on the act repairing engines now - none of whom have the organisational resources we have - nor their own in house machine shop (in which we have just fitted a CNC machine to keep manufacturing costs down), a World proven engine designer, racing reliability record nor (it seems) who can be trusted to fix faults if there were any they were responsible for (as we would if it ever happened). We are also just installing our own engine dyno test facility (so we can run rebuilt engines and cars under test conditions before completion) and are about to embark on another exciting internal engine development project to further reduce repair costs and increase long term reliability. We are also looking into the Cayenne engine problems that are emerging (that seem to have similar root causes) and expect that one day newer models will come our way for attention (hopefully in smaller numbers). Our aim is to maintain our reputation as the Worlds leading Porsche engine repair specialists and we are not sitting on our laurels but instead ramping up our continuous development and increases our material and personal resources while re-investing in the future. Baz

So to summarise, your quite sure you know the actual cause of all these engine failures & it can be attributed to oil viscosity, yes?

hartech said: I can tell you we are now regularly getting engines in for rebuild that have different designs of steel liners - that have failed. This not only supports our views (and clearly those of Porsche themselves who use exactly the same cylinder and coating as we do to rebuild our engines - in the GT2 and turbo engines) but it interestingly means that other businesses and owners are not going back to whowever provided those rebuilds (or they have refused to honour any warranty on their steel liner'd engines). There are a lot of others getting in on the act repairing engines now - none of whom have the organisational resources we have - nor their own in house machine shop (in which we have just fitted a CNC machine to keep manufacturing costs down), a World proven engine designer, racing reliability record nor (it seems) who can be trusted to fix faults if there were any they were responsible for (as we would if it ever happened). We are also just installing our own engine dyno test facility (so we can run rebuilt engines and cars under test conditions before completion) and are about to embark on another exciting internal engine development project to further reduce repair costs and increase long term reliability. We are also looking into the Cayenne engine problems that are emerging (that seem to have similar root causes) and expect that one day newer models will come our way for attention (hopefully in smaller numbers). Our aim is to maintain our reputation as the Worlds leading Porsche engine repair specialists and we are not sitting on our laurels but instead ramping up our continuous development and increases our material and personal resources while re-investing in the future. Baz I know Hartech are much respected (Include myself in this). But the above just sounds like an advert. In places it comes across as being written by someone with narcissistic tendencies. Personally, I'm pretty sure its for our peers to determine who is the best, not the company itself.. I'm sorry but that is how it comes across to me, and I think Hartech should be above this kind of thing. It's also interesting to note that it looks like the Cayenne engine is going the same way as most of the water cooled engines then. Anyway I won't come back to this thread. I'm about to get flamed to hell and back Edited by Wozy68 on Sunday 11th November 22:21

Baz,this is something I've been curious of after reading as much as I could regarding these engines and after fitting your Low Temp 'stat and a 3rd coolant rad I thought it was natural progression to fit an independent oil cooler but this brings me to the point that unless I'm mistaken you haven't ever mentioned fitting one as a matter of course even though it's due to oil temps that's scoring the bores. I know my engine failure was a different, rarer occurrence but I was thinking of fitting an external oil cooler to prevent bore damage. What's you thoughts? Edited by infrasilver on Sunday 11th November 22:27

infrasilver said: Baz,this is something I've been curious of after reading as much as I could regarding these engines and after fitting your Low Temp 'stat and a 3rd coolant rad I thought it was natural progression to fit an independent oil cooler but this brings me to the point that unless I'm mistaken you haven't ever mentioned fitting one as a matter of course even though it's due to oil temps that's scoring the bores. I know my engine failure was a different, rarer occurrence but I was thinking of fitting an external oil cooler to prevent bore damage. What's you thoughts? Edited by infrasilver on Sunday 11th November 22:27 No one mentioned oil, and the word does not appear in Hartech's last post either... did I miss something? The scoring issue as far as I recall is due to localised boiling of the water next to the cylinder as it circulates poorly and at too high a temperature.

Wozy68 said: I know Hartech are much respected (Include myself in this). But the above just sounds like an advert. In places it comes across as being written by someone with narcissistic tendencies. Personally, I'm pretty sure its for our peers to determine who is the best, not the company itself.. I'm sorry but that is how it comes across to me, and I think Hartech should be above this kind of thing. It's also interesting to note that it looks like the Cayenne engine is going the same way as most of the water cooled engines then. Anyway I won't come back to this thread. I'm about to get flamed to hell and back Edited by Wozy68 on Sunday 11th November 22:21 I can see how you might conclude this but trust me, hes a great engineer and a just a very proud man. He is so enthusiastic about his business and finding engineering solutions. It's what drives him to not retire! He has helped me on many occasions and has always given me his time freely (Grant also). You need to get to know him to understand him. MTR Edited by mollytherocker on Sunday 11th November 23:11

Globs said: No one mentioned oil, and the word does not appear in Hartech's last post either... did I miss something? The scoring issue as far as I recall is due to localised boiling of the water next to the cylinder as it circulates poorly and at too high a temperature. Yes, you even missed the first post it seems. The high temperature caused by the reduced cooling makes the oil temp so high that the oilfilm can no longer support the load between the piston and the cylinder, and then you get scoring. The cooling might be the cause, but the resulting reduction in oil viscosity and its ability to be a protective layer between piston and cylinder is what actually cause scoring.

gt3nor said: Globs said: No one mentioned oil, and the word does not appear in Hartech's last post either... did I miss something? The scoring issue as far as I recall is due to localised boiling of the water next to the cylinder as it circulates poorly and at too high a temperature. Yes, you even missed the first post it seems. The high temperature caused by the reduced cooling makes the oil temp so high that the oilfilm can no longer support the load between the piston and the cylinder, and then you get scoring. The cooling might be the cause, but the resulting reduction in oil viscosity and its ability to be a protective layer between piston and cylinder is what actually cause scoring. So if it's a boiling issue, what about that waterless coolant that made an appearance on Wheeler Dealers a while back?

The pistons rarely score the bores on the other bank of the engine (where the only difference is the temperature of the coolant due to asymmetric flow characteritics) and this suggests what we have found out - that by lowering the overall coolant temperature a little (so the thrust face on the vulnerable side now runs at the temperature of the reliable side) you can avoid problems on the critical side of the engine as well. While we do this by machining when an engine is stripped we cannot until is it so suggest a lower temperature thermostat as an easy to fix inexpensive alternative. We are not saying it can always cure the problem but that it must help. Using different coolant would not alter the temperature it is running at (which is controlled by the thermostat) and we see different failures with different causes even though the outcome of a scored cylinder is the same. One of those symptoms (local bubbling of coolant) only occurs usually if the system pressure has been lowered (by a leaking radiator or expansion tank cap). Regarding the accusations of being narcissistic - please allow me a full response - as I regard it as important. Firstly thanks for the support from some quarters and - don't worry Wozy68 - you have a right to your opinion and it does not bother me unduly and anyway I think there is some substance to your criticism. The problem for us is that we just happen to have the experience and ability to understand what the problems and solutions really are and provide reliable answers - yet the original manufacturer isn't helping people and there are a lot getting in on the act now that don't know enough themselves and don't seem to help after a rebuild if it doesn't turn out well. I am proud that at Hartech we regard our job as providing a reliable and ethical service for Porsche owners and we realise that it is difficult for them to know who to believe (and many are technically naive) so it is open for all sorts of people at all sorts of levels to exploit them (as some might argue has already been done at the highest level). All we try and do is provide enough information to help those owners in difficulties to make informed decisions. It is difficult to find a way to do that without writing about the success we have and the investment we are putting into this problem - to at least indicate how far advanced we are compared to others. This would not bother me particularly if they did a great job - but many simply do not and of course we see the results here when they come to us next and owners have to pay again for another strip, repair and rebuild (of which many who have had steel liners fitted elsewhere are typical). We are just trying to help people make the right decisions and to provide confidence to readers that the points we make are worthy of note. From my point of view – as a shareholder - I personally feel the implications of that investment into these engine problems as it presently runs at well over a 6 figure sum - money that the shareholders could have spent on other things instead (as so much of British Industry does - to the detriment of their long term future). So yes it is personal that we feel we are doing a good job out of this mess (that was not of our making) and a better job than many others who have exploited the situation. I guess that is narcissistic (and I am personally embarrassed about that) but if you don't blow your own trumpet - no one else usually will and I think we have honourable intentions in doing so. You will notice that often technical arguments appear on here demonstrating to us how confused and misinformed many are (and how easily their ill informed opinions could sway owners into blind alleys and poor decisions). It is unusual for a Porsche specialist to have our expertise and facilities and it probably does sound arrogant to state the facts (that I have previously designed and manufactured race winning engines and gearboxes and provided design solutions for most of the major Japanese and Italian manufacturers) – but it surely also means that when people don’t know who to believe they should put some store in that past success compared to some others and how are they to find out if someone doesn’t inform them. I think that coincidence of my background is beneficial to those with this problem and the fact that we have an IN HOUSE precision engineering workshop (to maintain quality control and speed up repairs) and have streamlined the stripping, repair and re-assembly of engines into an efficient production basis – is unique in our industry. I believe our 100% reliability record racing 2 Boxsters at the front of the pack in the Porsche Championship in 2012 is another demonstration of our ability and confidence that competitors simply cannot match – and surely it helps owners to be informed of the results of that “independent test”. Our recent investment in a CNC mill and engine test dynamometer also demonstrates that we are putting money into solving these problems and not merely trying to take it out (as some others are doing). Yes it probably is narcissistic to state all that and also that we do honour our warranty’s and would cover the cost of fixing a problem we contributed to (when we know a lot of others simply tell their customers what to do with their complaint). Yes it also benefits us through helping us attract business – and I would agree that there is a fine line between informing people and subtle advertising. What we must always remember is that the advertising medium is also an opportunity for those with less to offer to appear to provide just the same apparent quality to innocent owners caught up in this situation (but unable to separate the wheat from the chaff) - and if we decided to spend much more than them to advertise the differences in our case – the main beneficiaries would be the publishers and the cost would inflate our prices and defeat the objective for owners to keep costs reasonable. The internet does provide an opportunity to inform and there is nothing whatsoever stopping other engine rebuilders from contributing their technical know-how or presenting technical arguments to contradict anything we post (if they want to) to help owners choose their preferred supplier - the fact that they don't - in my view - speaks for itself. We feel that through providing such a comprehensive buyers guide (full of information and pictures about this problem www.hartech.org) and by spending lots of time trying to answer questions etc – we do enough to compensate for any subtle advertising we may be accused of – but I accept it is a fine line and I am sure others will think we occasionally step over it. If we have I can only suggest that this is preferable to having never posted anything about these engines and their problems on any internet site, nor to have provided a buyer’s guide to explain it all and to simply have left owners to the mercy of the market – which then would be able to con them unmercifully with technical b**l sh*t and sub standard repairs. I haven’t noticed anyone else trying to help in this way nor any other comparable technical explanations – so guys – try and be a little patient and a little less critical – we provide a good service to owners by having the knowledge and taking the time to try and help explain and if in so doing we innocently self promote – and some of you don’t like that – just try and apply a little generosity towards our intentions and have some patience with the outcome. We rebuild several hundred engines each year and you don't hear complaints about the results – so we must be doing something right. Those that know me well apparently often regard me as too modest for my achievements (and I prefer to be thought of like that) but no one can really judge themselves and if you think I am narcissistic at least the customers benefit from our hard work trying to be better than anyone else in helping owners with engine problems. If I am guilty of being proud of that - so be it. Baz

I haven't managed to do enough tests to answer with any certainty - but the following seems logical to me. Because under normal driving conditions the capacity of the coolant system to cool the engine exceeds the needs of the engine - if there is a lower temperature thermostat then the temperature of the coolant and all the internal engine parts will be lower when you are driving normally and the thermostat is controlling the flow and hence the temperature. Because of this the temperature will be lower at the moment you stop at say the lights and there will be less heat sink effect inside the engine. The thermostat will then not close as soon and therefore will aid the flow at standstill when the pump is idling and coolant flow is low - for longer. This will result in the temperature inside the radiators and connecting pipes and the engine being lower at any given moment - rising with time unless and until you have been stationary for so long that the temperature inside the engine gets too hot. You are right that at this point the fans should come on - but the flow is low at tickover so they will mainly cool the coolant in and around the radiator and not so much inside the engine. When you set off again the thermostat (being situated at the point of entry to the engine) only sees the temperature of the cooler coolant and so it takes a while to open again, This is the point at which the coolant inside the engine may well be very hot while it has not all found its way around to the radiators yet and back to the thermostat. So there is a period of time that you might be driving fast and generating a lot of internal heat before the thermostat notices that temperature rise and re-opens. This delay is not good for the internal engine temperatures. The lower the thermostat setting the longer it stays open and the sooner it fully opens again and so the sooner that flow rate is increased to re-cool the engine. So - to conclude - a lower temperature thermostat keeps the engine cooler for longer and starts to cool it off sooner upon restarting. There are arguments for re-setting the radiator fans to also come on at a lower temperature - but there are arguments against. If they cool the radiator coolant too quickly too soon you could get a flow of very much cooler coolant in the radiator and the pipes leading to the thermostat and these would then make the re-opening of the thermostat take longer while the engine may be being driven flat out but starved of coolant flow and when it does get through it may provide a higher thermal shock to the system. The combination of a long distance between the radiators and the engine, the thermostat being located on entry to the engine and the fans and thermostat setting all combine to try and provide a smooth system that naturally has a longer transitional time period during different driving conditions than with a lower temperature thermostat. If the thermostat was located at the engine exit - it would open sooner and protect the engine for longer. These issues are things that people rightly argue about and probably disagree about and it is not easy to provide a definitive answer without a huge testing program that we cannot afford to carry out (since we would need lots of specially prepared cars with test gauges driven for long periods to engine failure). All we can do is come up with a simple aid to try and reduce the incidences of failure through cylinder scoring. To do this we did fit temperature sensors to 2 cars (engines out stripped rebuilt and in again) and tested the cars with different thermostats in different conditions and then we stripped them - re-machined the coolant channels and rebuilt them and did it all again. We tested the fans coming on at different temperatures and then weighed up all the results and came to the conclusion that it was better all round just to fit the thermostat. I cannot claim these were the most sophisticated of tests nor that they were sufficient - but it is I think more than anyone else has done and the conclusions reached (and described above) at least have both theoretical and practical results to support them and I have not yet had anyone complain about the results of fitting the thermostat. The central radiator simply increases the potential maximum cooling capacity - for when and if it is ever needed - and is therefore a good thing in most circumstances. Unfortunately this is not an exact science in that some solutions would be better in specific circumstances and different ones in other circumstances. There is no perfect design answer except under repetitive identical use (like say racing). All we can do (and indeed all the manufacturer can do) is to try and cover as many possibilities as possible between a slow driver say in a very cold Country to a mad aggressive driver in a very hot one - is to try and reach the best compromise. I think our thermostat improves the general overall cooling and therefore is an inexpensive way to protect the engine more than leaving it standard - but it is a free Country and if you disagree - well just don't fit it and I will wish you the best of luck and reliability. Baz

if the problem is coolant flow rate would it be possible to use an electric water pump if such a thing exists in a similar model? probably many reasons why this couldn't be done but just throwing an idea out there.

anonymous said: [redacted] Not true, the stat will not be wide open except when the temp is too hot - at wide open the system is effectively out of control because it can't open wider than full. I'd be interested with any tests of the thermostat on the coolant outlet - it would be far quicker to react there.

anonymous said: [redacted] I don't disagree that when the rad fans are on the stat is open on a normal engine, but remember these stats are on the INLET to the engine, with a fan blowing the rads and a slow flow at tickover the water at the stat would be rather less then the temperature of coolant in the engine. I.e. the reason a cooler stat would work even for a fully warm car with fans going is because it's on the inlet side.

anonymous said: [redacted] Which makes a higher temperature stat close rather fast as this cool water tries to get into the engine. anonymous said: [redacted] On any stat arrangement there is a bypass or hole, you need that even when it's on the outlet. On any level it's difficult to comprehend the stupidity of putting the stat on the inlet side.

With most of the unit failures I've seen there has/is an underlying fault such as a leaky rad or failed exp tank cap or leaky exp tank this significantly lowers the boil temp and is magnified in any already hot spots .flow wise this is the thrust side of the engine the problem is made worse by mechanical weakness and being to close to thermal capacity IMO G

anonymous said: [redacted] The stat is regulating the temperature of the external cooling system - not the engine. As experiment shows a lower temp stat makes a difference, and that entirely fits with a regulated pipe and radiator temperature, rather than a regulated engine temperature. Simply put, the control loop is in the wrong place , and the engine isn't really in it. Your points - while valid, don't fix this, and the evidence shows it doesn't work.

Guys this is an enormously difficult system to understand and unfortunately I am away testing all day today so I don't think I have time to contribute until tomorrow. People assume cooling is easy - it is not an d I understand why the confusion exists. I will try and straighten it all out tomorrow as best I can - but meanwhile - it is interesting the differences of opinion that exist - all in their own way valid considerations. Don't all fall out about it - just keep tthe opinions coming and hopefully we cam get to the bottom of it. Baz

Globs said: On any level it's difficult to comprehend the stupidity of putting the stat on the inlet side. But they're not the only ones to do that.

Since beginning to realise that I had a problem with my Cayman S (06) I've spent some time reading this and other forums and in fact have probably read almost everything on the internet about the issues affecting the M97 engine particularly, but this family of motors generally. I realised pretty quickly that there are an awful lot of self appointed 'experts,' whose only claim to knowledge and experience is having read someones elses comments, or clicked a search on various headings, gaining a lifetimes experience on engineering subjects in about 50 milliseconds! Whilst this method of 'learning' can be useful, it as not all encompassing, neither does it equate to the knowledge and experience gained over a life as a motor engineer. It (for example) does not not give anyone the right to mock, ridicule or cast aside, such experience, research and commitment. IMHO there are only two companies (individuals) who have seen fit to thoroughly investigate, research and improve the problems which most of us, I suspect, have become too familiar. The other is in the US. My own experience of Hartech began only a week ago.I had engine noises, loud enough but not excessive, but high oil usage. My engine hadn't siezed, nor in fact did the water temp ever go up. Not much oil smoke either. They were very helpful over the phone, but really I knew what my problem was. It was just the extent that I didn't know. Well they took it apart and it was quite a bit worse than I expected, three cylinders were scored and the three pistons on the other bank were already losing the coating. Horrific. Big prob-big money. It was when I went back to them to discuss the options that I met Barry Hart. I have read all of Barry's thoughts and advice on his web-site (more than once!) I am not trying do gain any financial advantage in making my comments( well not really)!! Nor do I have any other connection with the company. I have to admit that I did raise my eyebrows-only a little!-at his response to certain people and comments. However I did realise the frustration that he must have felt at the comments of people who do not have his background and experience, neither have they invested the resources and efforts the he has over the years, (sometimes completely without result.) Barry's posts over the last 24/48 hours sum up his position precisely. It strikes me that some of the posters on this and other sites would be better beginning by reading Barry's site-and maybe a couple in the US- before passing their comments... and then reacting to his response! Winge over! I do appreciate that it is Barry's commitment to his engineering which, over the years, has allowed him to rationally approach various technical hurdles, faced by himself and others, and methodically found solutions. This is self evident on reading about his career and the successes. Be assured that there has been an awful lot of time and some failure involved in this overall success. Of course he has a financial benefit in his success, and rightly so, but my feeling is that the challenge of his work is every bit as important( maybe moreso) as any financial gain. He has virtually singlehandedly dragged these problems into the public arena, and not been afraid to publish his thoughts, the routes and processes taken and the results of his work, also enabling a wider discourse to take place. Whiuch in the long run can only be beneficial to us all. It is to their public shame that the great sports car manufacture Porsche, to whom we have all shown allegiance one way or the other, have been too arrogant and greedy, even to acknowledge that there are serious issues with these engines. Evidence the end of line M97 types(end of 2007?)one bought by the Police officer (Lady) from London with her one owner 10k example. Out of warranty, I suspect that Porsche only went back on turning her away because of her relationship with the supplying Dealership. The point being that the Company were quite happy to add a few figures to the list price in order to 'get rid' of the last of these vehicles from their stock, in the certain knowledge of particularly serious engine problems, which would affect a percentage of them! Having, as I have said, read extensively about the problems, I am confident that the approach and solutions offered by Hartech are the very best available. This work is not cheap, but is based on the cost of materials and time needed, and far better, and a t a more realistic figure than anything Porsche would offer. In fact it is frightening. I never envisaged such a cost in my ownership. I had no knowledge of these problems at the time I bought my car. I think there was very little talk about either. I did not buy my car, hoping to nurse it along, but to enjoy what had been advertised. That is a very fast, great handling, mid-engined car, unequaled-certainly at the time(better than the lesser 911 models-perhaps-wait for the avalanche!). How ironic, maybe, that that handling could be a part of the problem with oil movement away from Bank two. I did not buy my car to 'pose', but to enjoy the capabilities it is able to provide. I do drive fast and I do exploit the handling. (only where it's safe to do so!!!) I am lucky enough to be retired and enjoy driving my Porsche in France and Italy on some wonderful roads. Sadly very little in the last couple of years, while I worked out how I was going to afford to support the long term plans of Porsche. I am not engineer, but I have been a keen car person from a very early age. Sage advice from my father to my brother( who is also a motor engineer) and I, was to change the oil as often as possible, as this was a lot cheaper than taking an engine out for repair. My brother has always advocated the importance of warming up and cooling down (especially turbo engines) of your car, and continued the mantra of oil regular changing.(Surely this ought to be less so now with the modern super 'oils') The harder that the car has been driven, the more important. [ as an aside: I do know a little about engine building! having 'de-coked' the head from my A40 Farina and bored out and completely re-built my Sunbeam Alpine-together with my brother- 42 and 39 years ago!!] I don't state any of the foregoing as facts, only my reasoned thoughts based on my interpretation of both my own observations and other peoples efforts. I am prepared to discuss my own damage/rebuild if of interest to anyone.

Question for Hartech..... Apologies first if I have mis-understood your explanation. So could this happen to the new cars then ? As my interpretation of your explanation would lead me to believe the situation you describe is almost engineered into the new cars (981, 991) I'm referring to the 'Coast' feature. So you are driving with 'Sport' off so 'Auto Stop and 'Coast' are active, you are driving quite spiritedly using kick down, down a nice road for a few miles then you back off to slow down 'Coast' kicks in and the car drops to idle, isn't that the exact situation you describe ??

sorry to hear about your car and all 3 bores!being like yourself i had a failure(ims) about 6 years ago in a well looked after 986s and since then have read every thing i can on the internet but still went and bought a new gen1 cayman s early 2009 a run off instead of a more expensive gen2(saved £10k).i was fully aware of the ims issue at the time but had read later post 2006 cars have an improved bearing and failure is rare.the borescoring at the time was little known or should i say talked about on the internet.but over the last few years more cases have come to light so the end of last year i decided it was time to get a gen2 car and with good deals around too. the gen2 engine has no ims the engine is a closed deck construction and has an oil pump for each head,also cooling has been improved and they now use alusil liners instead of the lokasil in m96/97 engines.so hopefully a better long term allround engine and if you read planet9 they have raced the cars stateside with no issues unlike the gen1 and i have yet to read of a single confirmed issue with them and they have been with us for 5 years now. but i still think gen1 cars are great cars as long as you know about the pitfalls,budget for them and when something goes wrong send it to hartech for a rebuild and the engine will be better than when new Edited by itsybitsy on Tuesday 13th November 16:24

I always read with interest the posts from both barry and grant at Hartech. Having had a 996 with scored bores that required a rebuild i greatly appreciated all the help and advice they gave me. Their knowledge is priceless and the fact they give it so freely speaks volumes about them as a company. It always amazes me when they take time to post, just how many "experts" pop up to question their views. However i have yet to hear a bad word spoken about them by anyone who has actually used their services. Perhaps Porsche should be as vocal explaining the engine problems, perceived or genuine.

cmoose said "so long as it's done in a honest attempt to understand better. If something doesn't seem to add up, why not put the question? Everyone is then better informed." I totally agree, but a lot of the time the comments above dont apply

I wonder if somebody has taken this issue to consumer rights organizations who govern issues with manufactures responsibility outside warranty. Of course the whole issue is hard to understand but clearly this is not an case which other makes have, which would be a case for manufacturers fault. It is kind of sad that Porsche has not had much bad press in this. Usually automotive press gets active only if there is people in danger because of the fault.

churny said: I always read with interest the posts from both barry and grant at Hartech. Having had a 996 with scored bores that required a rebuild i greatly appreciated all the help and advice they gave me. Their knowledge is priceless and the fact they give it so freely speaks volumes about them as a company. It always amazes me when they take time to post, just how many "experts" pop up to question their views. However i have yet to hear a bad word spoken about them by anyone who has actually used their services. Perhaps Porsche should be as vocal explaining the engine problems, perceived or genuine. Nothing wrong with questioning. Everything that Hartech posts makes sense but some things still remain unproven and one shouldn't assume that everyone else is ignorant of this subject. And we shouldn't forget that Porsche have one or two well qualified engineers of their own, yet we are expected to trust everything that Baz says without questioning to understand better, as we castigate the Germans for building a crappy engine? Interesting to note that all six bores of the Cayman discussed above were damaged. Not just certain sides/cylinders then? That's the first time I've heard of that.

REALIST123 said: as we castigate the Germans for building a crappy engine? Actually the blame is partly on us Finns who built all gen1 caymans and boxsters (and most of gen2 versions)

REALIST123 said: Interesting to note that all six bores of the Cayman discussed above were damaged. Not just certain sides/cylinders then? That's the first time I've heard of that. Except that's not what he said...

Raitzi said: Actually the blame is partly on us Finns who built all gen1 caymans and boxsters (and most of gen2 versions) No, it wasn't the fault of the builders, it is the design that is cheap and poor.

mollytherocker said: Raitzi said: Actually the blame is partly on us Finns who built all gen1 caymans and boxsters (and most of gen2 versions) No, it wasn't the fault of the builders, it is the design that is cheap and poor. Absolutely. The Finns are just building to Porsche specifications.

anonymous said: [redacted] I realiae the warranty point but am still intrested in any failures of 991 OPC or otherwise.

Sorry Baz but a poster mentioned here handling potentially affecting oil flow?Do you see any connection?

REALIST123 said: Nothing wrong with questioning. Everything that Hartech posts makes sense but some things still remain unproven and one shouldn't assume that everyone else is ignorant of this subject. And we shouldn't forget that Porsche have one or two well qualified engineers of their own, yet we are expected to trust everything that Baz says without questioning to understand better, as we castigate the Germans for building a crappy engine? Interesting to note that all six bores of the Cayman discussed above were damaged. Not just certain sides/cylinders then? That's the first time I've heard of that. Don't think anybody said the Porsche engineers aren't qualified infact they probably all know the problem but they are not in a position to do anything about cars with problems! I have the hans mezger autobiography Porsche and me and in the last chapter he talks about the new 996 and how it should only have had one engine for all models including turbo and gt3 but the engine which was designed wasn't strong enough, and how the company had changed and become very profit orientated etc etc the way I read into it was Porsche new all about this problem but choose to ignore it! With regards Hartech they are the best in the business.

So who is responsible for this flawed and cost driven design? Harm Lagaay, who oversaw the 996/Boxster project? Or was it Wendelin Wiedeking who took over at Porsche as CEO in 1993 and revolutionised Porsche by introducing Toyota style lean manufacturing? It is well documented of course that he 'saved' Porsche from extintion, due to its expensive hand built methods and over-enginneering. I believe that the 996 cost half to make than the 993. But looking back and seeing where Porsche is today, maybe it was necessary, certainly Porsche is healthier than ever and we have still had some great cars since and hopefully many more to come.

itsybitsy said: sorry to hear about your car and all 3 bores! being like yourself i had a failure(ims) about 6 years ago in a well looked after 986s and since then have read every thing i can on the internet but still went and bought a new gen1 cayman s early 2009 a run off instead of a more expensive gen2(saved £10k). i was fully aware of the ims issue at the time but had read later post 2006 cars have an improved bearing and failure is rare.the borescoring at the time was little known or should i say talked about on the internet.but over the last few years more cases have come to light so the end of last year i decided it was time to get a gen2 car and with good deals around too. the gen2 engine has no ims the engine is a closed deck construction and has an oil pump for each head,also cooling has been improved and they now use alusil liners instead of the lokasil in m96/97 engines. so hopefully a better long term allround engine and if you read planet9 they have raced the cars stateside with no issues unlike the gen1 and i have yet to read of a single confirmed issue with them and they have been with us for 5 years now. but i still think gen1 cars are great cars as long as you know about the pitfalls,budget for them and when something goes wrong send it to hartech for a rebuild and the engine will be better than when new efp.

Interesting hand bagging over the thermostats guys! My observations following basic science lab testing of my 996 stats... -with some boiling water tests plus thermometer I was amazed at how little they open thus they present quite a flow restriction, which we don't want. -the design is basically 1950s or earlier, simple, basic tractor naff, my E46 BMW of the same era has an electrically assisted stat, to give I reckon increased opening, controlled by the DME -anybody know more? -the Hartech stat works very well, opens earlier which makes bleeding easier and crucially has a much greater sized copper core, so greater surface area and thus faster response -just what's required. Best we can do really without retro fitting a BMW thermostat, which I was pondering on! Wish I had the time to find the silver bullet on this one!

No hand bagging fiddler, in this PC world you may have failed to recognise a good natured yet robust discussion. One thing I did notice about the 987s I borrowed was the warm-up time being very fast, maybe they concentrated on that too much? Interesting about the Hartech thermostat being rather better than the asthmatic standard one, that would work in cmoose's 'fans on, wide open' traffic light sweating scenario. If I was DIYing this I'd rip out the inlet stat and put an inline one of a decent size right at the outlet

All the technical stuff aside, and I am (was) an engineer, I still can't grasp the fact that Porsche designed an engine that had insufficient cooling. I am not aware of any other engine made in living memory that could not cool itself in all circumstances. This is the company that has produced some of the best engines ever made. Thank Christ they recognised it quickly and retained the GT1 block for the real cars.

mollytherocker said: Thank Christ they recognised it quickly and retained the GT1 block for the real cars. Quickly? 1998 - 2008 - I make that a decade of not recognising it... and the IMS, D-chunking and odd RMS weep..

For'ITSYBITSY' thanks for your comments. By all accounts I think that you are pretty safe with your car, I hope so. If forewarned and the purchase price reflected the potential problems, then maybe you would be in a position to make a choice, not sure that anyone would-unless the car was dirt cheap. Sadly I was not in that position and certainly I didn't become aware of the probs for about 3 years, as I suppose many others didn't. Now in the position of paying a huge figure and keeping the car-probably.

Globs said: mollytherocker said: Thank Christ they recognised it quickly and retained the GT1 block for the real cars. Quickly? 1998 - 2008 - I make that a decade of not recognising it... and the IMS, D-chunking and odd RMS weep.. It took less than a year to recognise that this engine could not be raced as it was made of cheese. The 1999 GT3 was fitted with an old engine that was deigned properly. But your point is valid in that it took them 10, yes 10 years to consign this engine to the skip!

anonymous said: [redacted] I guess you are right. They knew what they were doing with the m96. This was not an engine designed to do Le Mans and then drive home. It had a very different intent. And that is a shame. And they could have fixed these issues relatively easily and chose not to. For 12 years! Not good.

Ian_UK1 said: REALIST123 said: Interesting to note that all six bores of the Cayman discussed above were damaged. Not just certain sides/cylinders then? That's the first time I've heard of that. Except that's not what he said... You think the pistons could lose their coating without there being some damge to the cylinders? Why did the coating wear then?

mollytherocker said: They knew what they were doing with the m96. Respectfully I'll disagree with that. The engine was built to a price, but the same price would have built a far more robust one, the main changes needed were: 1) IMS bearing that oil could get to. 2) Enough cooling flow past the cylinders 3) A better RMS seal 4) Slightly thicker cylinder walls 5) Closed deck (maybe not necessary with decent cooling). After year 1 they could have set aside a team of 2 or 3 people, solved the problems, and their investment would have been repaid many times over. It's not just schoolboy errors in the engine design detailing, it's really a management failure to rectify the mistakes. Maybe they were too focussed on buying VW and sales figures to look at their own quality issues.

I wanted to avoid getting into too much detail because it seems to result in even more arguments from those that rarely actually know much about the cars and have never conducted any tests – but since we are getting to a point where it cannot be avoided – the following is how I explain the results of the tests we carried out here. Please remember when reading it that my tests showed an improvement that I was seeking. This explanation is how I understood the way it all was working. My explanation may or may not be right but that does not invalidate the test results - which have to stand unchallenged until someone else does similar tests and has different results. You may therefore argue about my explanations but there is no arguing about the results of the benefits of fitting the lower temperature thermostat. I don’t know if anyone has experienced an old car with w head gasket or coolant pump problem but if you have you may remember that they usually boil when you stop driving them. This isn’t just because of the lack of air flow but mainly due to heat sink back into the system. When the revs drop and the air flow (i.e. stationary) there is a lot of heat sink in the engine parts that had been stabilised by high coolant flow through radiators cooled by high air flow through them and over the car in general. As the revs drop the coolant flow reduces considerably but the heat sink effect continues to flow heat inside the metal that was passing through it towards the coolant areas into the coolant in the upper engine area and because the flow is reduced the coolant temperature rapidly rises. Similarly because of the reduced engine speed the oil pressures falls and the oil that is sprayed into the cylinder area to cool and lubricate the pistons and cylinder walls (through valve’d oil spray jet nozzles) stops reaching piston and cylinder wall which locally overheats the oil there and its viscosity falls dramatically. Because the pistons sit horizontally this very thin oil separating the piston from the cylinder wall drops lower down the piston through gravity and starves the top (which on bank 2 is the thrust face). At the same time the oil in the cylinder head area similarly gets hotter but is not cooled then as it flows back through the oil cooler because the coolant flow in that has also reduced considerably with the revs drop. This heat sink effect not only feeds back into the slow moving coolant but when this hot coolant finds its way slowly out of the cylinder block into the outlet channels it can trigger the fans (via the temperature sensor and the ECU control). But there is not a fan temperature switch located at the fans (as you saw on older models) only at the engine outlet – so there is no control of the temperature of the coolant through the fans and no control over the resulting temperature leaving the radiators. Although you could argue that the coolant must pass back into the engine and up to what is effectively the fan switch again which will only switch off when the coolant temperature is low enough – you forget the consequence of the heat sink effect from the engine which initially floods the coolant now slowly moving through the engine with heat – so the fan can still be switched on when the coolant leaving the radiators is quite cool. The thermostat (like all control systems need) has a built in damping effect that slows its response to temperature changes - so sudden temperature changes do not result in an instant response. All control systems (whether regarded as open or closed loop systems) have an element of damping or inmertia that makes them work differently under different inputs and extrenal influences. It is rare to find a p erfect control system for all eventualities. In my opinion (and my tests confirmed this) the cool coolant returning from the radiators to the thermostat starts to close it and this reduces the flow further but the heat sink in the engine parts continues to add heat at a high rate compared to the reduced flow and this results in the fans staying on even though the thermostat is not wide open and the engine may be ticking over or even switched off. As a result - when you set off fast again - the coolant flow towards the thermostat is too slow initially and the coolant that has passed through the radiator slower and is therefore cooler - and this delays the full opening of the thermostat further. Eventually this makes the coolant in the engine that is already hot (and may well have started to bubble up and temporarily air lock - too hot) - because it has not yet got round to the radiators or back to the thermostat which has not yet opened quickly enough. This is the danger point at which scoring can occur when the driver sets off fast again while the oil near the pistons and cylinders is still too hot and thin and the torque is high at the low initial revs. In control system speak the damping of the thermostat is not capable of responding at the right speed for all eventualities and the one time it seems to respond poorly is when the car has been stopped from a fast run for a short while and then sets off fast again. If the car is stationary for a lot longer – eventually the thermostat stabilises its position as the heat from exhausts etc rises (with lack of cooling air flow) and the coolant temperature does then rise throughout the system and the fans switch on and off to stabilise the system – but it does not manage it after short stops and starts. We designed our themrostat to try and respond better in these conditions and our tests showed that it worked. Please also remember that the temperature gauge on the dash board not only reads incorrectly and too low at temperatures above 80 but the system feeding it with information to move is also damped so you cannot rely on the readabkle output as a means of constructing a definitive argument about actual temperatures. I only discovered all this by fitting a number of quick reaction temperature sensors and gauges to different parts of the engines and recording the results for analysis later of different driving situations. I am not claiming that those tests were conducted under the best of test conditions that say a manufacturer may be able to conduct nor that they were fool proof but they indicated to me that the lower temperature thermostat kept the cylinder temperatures lower and was quicker to respond under all driving conditions and this in turn is a benefit. At least I was able to read reliable temperatures and compare them for each different thermostat. I am also glad that the responses demonstrate to me exactly the point I was making earlier about adding the qualifications people have for making them – to posts (even though I get accused of Narcissism). For example - I think that if I had stated my credentials and test results and the feedback from customers etc etc and then stated what I think - and A N Other stated they don't actually know where the thermostat is placed in the engine nor how the system works - but then went on to suggest my findings are wrong and their theory is right - more people would be able to judge who is most likely to have worked out the right answers. In response to the "coasting" question - I do think it is unfortunate unless the system has been adjusted accordingly (and have not tested for this). The whole subject of engine cooling seems simple in some ways (in how it can be designed and built) but perhaps you can now see that it is extremely complex in how it works under different driving conditions and that there is a lot to think about in the system that effects it. I personally think that if an engine has a cooling problem - then the themostat would be better placed at the engine outlet (even though this makes it take longer to warm up and therefore uses more fuel). Many system by the way do not have bypass holes (although a simple drilled hole in the thermostat - as they all used to have - assists continuous flow in low pump speed situations – but admittedly slows warm up times which is something manufacturers seem to be trying to reduce). Centrifugal pumps are also notorious for providing slow flow at low revs but are great at delivering full flow variable with the resistance at higher revs (or thermostats at opening) and do not cause the problems that a displacement pump can cause - but they are poor at low revs especially when the bearing wears and the close clearance between the pump blades and the housing deteriorates - even a small amount (as they do with age - having plastic impellors). All I was interested in was finding out the temperature inside the engine where the problem takes place (inlet and outlet of the cylinders and heads) with different thermostats and under different driving conditions and the results proved to me that lowering the thermostat temperature improved and reduced cylinder temperatures and temperature change response times under all conditions I could reproduce. The UK was not hot enough at the time to run the engines above their maximum designed capacity so I cannot comment on what might happen if I could. With all due modesty - until and unless someone else goes to all that trouble to strip and rebuild and test engines several times with temperature sensors in them and under different designs and conditions - I think it is unhelpful for people to contradict what I found out. You can argue about the theory and expectations as long as you like but you cannot argue with my results until you have similar but contradictory results of your own – so for the sake of readers who really don’t understand any of this and simply want guidance to do something to protect their engines – (and while I am all for debate and am not always right etc etc) please try and resist having strong contradictory opinions about all this if you do not even know how the engine cooling is laid out or how it works but just have a theory to regurgitate - as there is nothing to compete with practical test results carried out on the actual cars in question as I have done. To argue that Porsche have well qualified engineers there as well seems incredibly stupid when the whole debate is clearly about something they didn't manage to get right. I have recently been informed (but have no way of verifying) that the new chief buyer at Porsche came from a washing machine manufacturer but when he was found out for buying in a cheap copy of a well known part - he was sacked. I must say this scenario does seem to fit some of the issues we see. I really don't mind debates at all and I am often wrong in the many technical ideas I have and solutions - but I always test things out and strangely being prepared to be wrong sharpens the intellect and sustains thorough testing until a really good solution is found. On this issue of engine cooling we came up with a simple inexpensive inmprovement that our tests results supported - but it is a free Country and you can please yourself if you fit it or not. We will never recover the test costs throuh sales of such an inexpesnive part - but at least it has improved the reliability of engines we rebuild and I think has helped some others yet to fail to avoid it all together. While testing at Oulton Park yesterday - I was accused of fitting lots of special parts inside our Boxster engines to make them as quick as they are and reliable. Can I just confirm that we purposely took a risk to run with standard Lokasil cylinders and Porsche pistons but did modify our coolant flow and used the low temperature thermostats (and the third radiator) with 100% reliable results - and we did this because for us racing is our way of extreme testing (that would be impossible, dangerous or illegal on public roads). Baz

Very informative post Baz - when you fit a low temp thermostat do you also change the location to the engine output side?

Hi Baz, Again, a massive thank you for your time is letting us know your thoughts. I for one, have NO idea how cooling works. I am looking to buy a Camyan 3.4S in the next few weeks, is there a package you can put together to help with cooling. (Feel free to PM/email me, inc fitting) Things like? Low temp thermostat (moved if required) Centre rad Oil change to the best grade you feel would help etc.. Thanks and I look forward to hearing from you. Dan

The coolant sensor is on the casting (at the opposite end of the engine to the flywheel) that collects the coolant before sending it on to the split pipes feeding the front radiators. It is actually lower down than the highest point inside the engine where the coolant can sit. The control is through a DME. I have not yet found out what it looks at to switch on the fans. Perhaps someone else can confirm this. To solve problems like this with our comparatively limited resources - force us to make calculated pragmatic decisions and once we had tested the benefits we were seeking and confirmed that we had achieved them (both in test results and in the resulting reliability of engine rebuilds etc) having to explain all the intricacies of the system is a kind of afterthought for the interest of readers and to counter claims by some that fiting the low temperature thermostat is somehow wrong. I think I understand it all very well but if not - the test results still supported the fitting of the thermostat (and other changes we made as well). Both cars that were used in the tests are still driving around OK with the temperature senders still fitted but not wired in anymore. We may very well reproduce some of these tests in the racing cars for next season because our development oprogramme with Millers Oils has raised a few points they need testing for which the exact oil and coolant temperatures are relevant - so we may get further with our understanding of all this next season. Baz

For someone working towards that First Porsche Ownership moment this has been a hugely useful thread and although I have had to go back and think about Baz's explanations at times it does make sense. I can see how a localized hotspot could occur at one end of the engine flow and then work its way back up the system and that seems very clearly to match the pattern of engine damage. Low coolant flow is bound to lead to large temparature differentials within the system when there is a lot of heat to get rid of and not much airflow. I can also see why having the fans whirring does little to benefit the engine since the heat is building up elsewhere and the damage is done before the cooler coolant arrives there. The low temperature thermostat keeps the whole system slightly cooler so there is more heat absorption capacity in the system overall and hence greater overhead if a localised heat build up occurs. So two questions for Baz. 1. the explanation is great but it is still a little unclear to me what real life driving conditions are likely to trigger a problem. I appreciate that it is a hot engine held stationary for a while and then revved hard on getaway but how hot, for how long and revved how hard? An idea of a typical danger scenario would be useful. You mention a stop at lights as being the most likely cause of problems but would that be something like coming off a motorway having run at 70mph+, stopping at a set of lights and then caning it away onto a dual carriageway? Or could it be triggered by trundling around town where the engine revs are not so high but the air flow is minimal and then doing the show off burn out from the lights to impress the public? And how long a stop would become risky? Some motorway/dual carriageway exits now have multiple sets of light where you can at times end up sitting stationary three times on the bounce before you get off the roundabout. That builds up the frustation so when the last set goes green the right foot gets a bit heavy and suddenly the bores look like a ploughed field. For anyone who knows it the A2/M25 junction going away from London and then south on the M25 seems to be a typical example. Lights off the A2, more lights under the motorway and another set of lights controlling the flow between the roundabout and the A2 westbound. That is followed by a mad dash onto the M25 filtering into traffic doing 70 but with no spare lane for slower vehicles already on the motorway to move into. The process of slotting into the motorway flow often requires a hefty dose of acceleration. From Baz's explanation that sounds like a prime candidate for damage. But what about cross roads? Would a brief stop at a give way be a potential hazard? 2. the main issue actually seems to be coolant flow. In addition to the low temperature thermostat is there any alternative to the existing pump so that a greater speed of flow is maintained at low revs? It seems that so long as the coolant is moving there is ample capacity in the system so it would not require much additional push. Or possibly a larger bypass? Hopefully with all of this useful background info when the FPO moment does arrive it won't be followed shortly afterwards by the sound of a grinding engine

Cmoose the answer is "yes". Bill - I would love to be able to answer all your specific questions but it is practically impossible to assertain exactly when the problem occurs. To achieve this you would probably need a camera somewhere inside the engine recording the piston face (or the cylinder bore as the piston rises) and then linked to a data monitor time phased to pinpoint the exact circumstances under which the sudden initial scoring occured. We certainly could not undertake that. So we have to imagine from experience - what circumstances would logically lead to a problem. We know tiptronics have a greater incidence than their numbers - and they drive off in 2nd with higher low rev torque. We know cylinder scoring is more prominent at low revs and high torque. We have proved that at high revs they seem to work OK. We have tested an engine in a way to make it score and it did so as expected and then we have to intellectually consider what is going on (as described above) and try and make sense of it all (which I think we did). It is almost impossible and therefore only opinion - but what is not up for discussion is the fact that with the lower temperature thermostat we found more stable lower engine temperatures and this is better than higher ones. We must remember the temperature rise by the time the coolant reaches the top of bank 2 is not much higher than that on the thrust face in bank 1 - yet is the difference that causes the problem so it is logical that a small reduction could protect the engines. I am now not really sure why I ahould have to keep answering specific questions that may enable someone else to keep arguing about out test results - unless they have some as well. Very short periods staionary should not be a problem - any over 1 minuite might be - I don't know but it makes sense to me to drive off without full power at low revs if you have been staionary for a while - just through a few gears to allow the coolant to circulate and the thermostat to respond and settle down before caning it. Baz

Think you've provided enough info Baz - you could be posting on here for forever and a day and questions will still emerge. It's such a cheap fix, that if I was running a 997 etc. I'd be straight down to yourselves to get a 3rd radiator fitted and the low temp stat.

Hartech, I read your web info on the saga, and, I would like to throw my spanner into the works for your perusal. I have some 'in service' experience with top flanged cast iron liners and the thrust anti-thrust cavitation that can result, waterside, from air bubble collapse due to liner vibration. The liner set up is inverted in the case of the engines you have in question and your current machining 'fix' does indicate that some liner movement would seem to be evident, especially on the larger bore units, i.e. those with a thinner wall section. I am not au fait with the sealing of the cylinder head / liner face, are there any indications of fretting when particular cylinders have shown major distress? What is also interesting is your view regarding water flows and the system the OEM has employed. Far be it for me to question their design effectiveness, but, having taken part in many engine installation reviews on heavy duty automotive diesels I can say with conviction that water flows around an engine installation do not necessarily go where you think they do once thermostat's start to modulate. Have you used sight glasses wherever possible, on your test bed cooling system set up to ensure the OEM layout deaerates correctly and the water flows as it should through the system from a cold start up to a full full power curve, and in the correct volumes. I hope I have given you some food for thought, if not I'll shut up.

Baz, would there be a problem if say you were racing your water cooled Porsche and had to do a compulory pit stop. I think the stand still for up to a minute could replicate the damaging conditions you outline. I race in a series that has these pitstops, I've an aircooled 993 so hopefully I should be ok?

Baz You have me convinced and thanks for all of the effort you have put into this. I used to think all 911's were just about indestructible. Then I started reading the forums and became convinced they were as fragile as egg shells, especially in the range that I might be able to afford one day. Now at least I feel there is someone who has an answer and I really can work towards my serious mid-life crisis sports car. So I think I have a clear idea of what to do (i) find a car I like (ii) find a way of affording it and (iii) hand it over to you to do the necessary It is just that (ii) is causing a bit of a problem at the moment, but it is only a matter of time...

hartech said: But there is not a fan temperature switch located at the fans (as you saw on older models) only at the engine outlet – so there is no control of the temperature of the coolant through the fans and no control over the resulting temperature leaving the radiators. Thanks as always you the information you share Baz, I'm stunned by yet another basic error now! So they broke the control loop for the thermostat by putting it on the inlet (duh!) and broke the control loop for the fan by putting the switch on the outlet (duh! again). On top of the incorrect head/cylinder wall coolant flow ratio. I can see why your lower temp/bigger flow 'stat makes such a difference now, with such a broken cooling system backing off a few degrees is the safe and prudent thing to do. I still have difficulty in understanding why the Porsche engineers committed a) such basic schoolboy errors and b) left it like that/made it worse over a decade. Amazing.

Baz. Are you seeing any later engines or any decrease in failures,also (dont feel obliged to answer) have any/many of your rebuilt engines failed? Have you done any work on 991 yet or indeed DFI 997 and are there any noticeable improvements to the internals worthy of mention? Ive just seen one with a thrust side rattle. Sorry for all the questions but there are limited sources of this calibre information. You take the critisim well you just cannot help some people! Thanks Baz Edited by Gary11 on Wednesday 14th November 21:16

Great info here & thanks for persevering with the posting Baz. On a side note here, Regarding the IMS bearing failure. I understand the theory of replacing the bearing with ceramics & removing any seals on them, but has anyone considered machining a carrier which could utilise the bushes from the turbo / GT3? Surely this would be a "belt & braces" approach & possibly a final answer?

static2010 said: Great info here & thanks for persevering with the posting Baz. On a side note here, Regarding the IMS bearing failure. I understand the theory of replacing the bearing with ceramics & removing any seals on them, but has anyone considered machining a carrier which could utilise the bushes from the turbo / GT3? Surely this would be a "belt & braces" approach & possibly a final answer? The GT1 engine used in the GT3 and turbo doesn't have an IMS.

The turbo and GT3 engines do run an intermediate shaft, but it uses white bearings, running in oil, I beleive that was what the guy above you was suggesting converting too.

I fitted one of Baz's low temp thermostats (with the additional 3rd Centre radiator kit from Porsche) to my 997.1 C2S. What I saw instantly was an oil temperature that was consistently lower and when used hard, the oil temperature didn't get anywhere near as hot (10 Degrees lower than previously despite the same ambient temperatures and driving style on the same roads). Equally at a hot idle, the oil pressure was 0.5 bar higher on the gauge. The obvious conclusion was that as there is an Oil / Water heat exchanger, it was all running cooler ....

MadMark911 said: I fitted one of Baz's low temp thermostats (with the additional 3rd Centre radiator kit from Porsche) to my 997.1 C2S. What I saw instantly was an oil temperature that was consistently lower and when used hard, the oil temperature didn't get anywhere near as hot (10 Degrees lower than previously despite the same ambient temperatures and driving style on the same roads). Equally at a hot idle, the oil pressure was 0.5 bar higher on the gauge. The obvious conclusion was that as there is an Oil / Water heat exchanger, it was all running cooler .... Well, as you say, the conclusion was obvious. What were/are the running temperatures of your oil and water and you OP then?

Steve Singh - no we leave it where it is - too expensive to modify the system otherwise. Dan 911 - Don't think you need the central radiator - just the thermostat - but could work out a cost while doing one - difficult to quote on otherwise. SValve - There are no seperated liners - they are homogeneously cast in. Fretting does occur in the 944 and 968 models throught the tops of the open deck liners expanding and contracting under the thrust loads - oval and round again. Porsche knew this and fitted a head gasket with circular cut outs in 2 of the three steel head gasket sheets (top and bottom) so that movement didn't break the thin plastic coating that ultimately seals the head (photo in our buyers guide engine sections). Cylinder coolant capacity has been reduced with each newer model as the block height and general internal space is the same as from, the 1st 2.5 engine so as each bore increased so did the cylinder capacity get reduced and as the stroke was increased so the thrust angle to the cylinder bore has increased together with the actual thrust from the bigger engine and the advanced variocam 2 system. Meanwhile have you seen the small inlet holes to cool the cylinders (again photo and explanation in our buyers guide engine section) that allows only a very small percentage of the total coolant to pass through the cylinder block and therefore slows its speed and increases the temperature gradient across the engine. Tie that in with the drawing explaining how the thrust face is hotter on the side of the engine that fails and the whole picture becomes much clearer. Globs - yes from what I know of control systems - this is bound to cause problems under some conditions - because there is no control over the amount of cooling from the fans to the coolant temperature returning to the thermostat and due to the damping speed of movement of the thermostat - the system can go out of control - hence our different design with a bigger central expansion core. Static 2010 - The original white metal shells used in the older 911 engines and the GT3 and Turbo's version of their intermediate shaft would need to be pressure fed from the oil pump and this would be very complicated to achieve. In those earlier models it only drove the roller chains at one end of the engine so was not subjected to the same torsional stress. Furthermore the hivo chain used in later models is heavier than a roller chain so would need more substantial support. Conclusion - this is a step too far. The later shaft for Hivo chains with the larger bearing cannot be fitted to earlier roller chain crankshafts so also need a new crankshaft. However we are testing a new Intermediate shaft we are manufacturing that we have designed both for Hivo and roller chain ends and uses the larger bearing but without the seal and this will retail much less expensive than the Porsche replacement and I expect it to be a permanenet solution. As with all the problems these engines incorporate - the vast majority still survive OK and so these discussions about mistakes and quality issues show that in terms of making an engine to perform well and cost less to manufacture - the Porsche engineers did a great job. Indeed if the failure rate was ever discussed and found acceptable - they did what they were instructed to do. It would have been so easy to fix the problems in subsequent engine upgrades (when in fact in some cases they got worse) and it is difficult not to consider that the designed in general life expectancy may well have been established and achieved. They are after all still in business after making huge profits and still selling new cars and seem to have preserved their reputation despite some poor design elements in these engines. Personally I think they were just design ideas that a younger team thought up and assumed would work that testing under the ideal conditions of a factory test driver did not show up in enough numbers to do anything about retrospectively and that once the true scale of the problems and the costs to customers that resulted - became apparent - it may have been thought better to tough it out than experience the reduction in brand image that an admission and some compensatory device may have resulted in - re-design a new model without the defects and hope that it all goes away - which has pretty well worked. They must be thick skinned because just through the coincidence of my background enabling me to find cost effective solutions and our presence in the Porsche market - we feel an obligation to try and minimise the cost of fixing these problems and improve the resulting reliability that clearly isn't bothering the business that created the problem. I also feel an obligation to try and help owners understand the problems and trust in good solutions while being able to be sufficiently informed to stand up to attempts to con them into decisions that result in choices for a repair that are more expensive in the short or long run and less reliable - although at times - when I find misguided arguments apear that simply confuse owners - I wish I was more thick skinned and could just ignore it and get on with my work here at Hartech. Baz

gtphile said: The turbo and GT3 engines do run an intermediate shaft, but it uses white bearings, running in oil, I beleive that was what the guy above you was suggesting converting too. Sorry, I knew that the small shaft in the GT1 engine was so different in both size and how it works I didn't realise it was actually called an IMS as well.

REALIST123 said: MadMark911 said: I fitted one of Baz's low temp thermostats (with the additional 3rd Centre radiator kit from Porsche) to my 997.1 C2S. What I saw instantly was an oil temperature that was consistently lower and when used hard, the oil temperature didn't get anywhere near as hot (10 Degrees lower than previously despite the same ambient temperatures and driving style on the same roads). Equally at a hot idle, the oil pressure was 0.5 bar higher on the gauge. The obvious conclusion was that as there is an Oil / Water heat exchanger, it was all running cooler .... Well, as you say, the conclusion was obvious. What were/are the running temperatures of your oil and water and you OP then? Hard running in summer ambient temperatures (but not track work) would move the oil temp up to about 105 Degrees before - never over 95 degrees after the work was done. Normal running in the same ambient temperature used used to show about 90 degrees oil temp before and 80 degrees after the changes. Oil pressure after a fast run used to be 0.75 bar before and 1.25 bar after. After a more gentle run (but still hot) it would be 1 bar before and 1.5 bar after.

If the problem is the breakdown of the oil at the upper end of the temp scale, is there not a more durable blend that will be a suitable replacement to protect the bores at higher temp ranges? What do seasoned races use and assuming it's porsche approved, is it not the other way of solving this? Or have i over-simplified the matter and so missed something somewhere?

Cylinder scoring is more prone to occur at low revs & high loads - typically pulling away with large throttle opening but low revs. When racing you are never using such low revs and the road speed of the car is always reasonably high - hence air flow both over the car and through the radiator aids cooling. It is therefore unlikely to be aproblem for cars at racing speeds on tracks. Some special oils have additives that only release or work well at temperatures over 90 or 100 degrees but the cylinder problem is only likely to occur at the piston face when the temperature is higher than that locally - so should still be OK (but worth checking). It should always be considered that the standard oil tests for viscosity are carried out as a flow rate through a hole at various temperatures. The engine parts (pistons to cylinder, crankshaft shells etc) all apply pressure to a face between which is oil. The hotter the oil, the lower the immediate local viscosity and the quicker it leaks out of the gaps between the piston and cylinder bore or shells and crankshaft journals - so the less remains to support the components and keep metal to metal apart. Although the typical viscosity tests are similar they do not work exactly the same and the high temperature of a piston feeding through the oil to touch the cylinder wall and then go on from there to reach the coolant results in a much higher local temperature (and much lower viscosity) at the piston face than the mixed oil will have as it returns to the oil pump and through the oil filter and oil cooler. Baz

Baz would a bit more oil pressure help,ive noticed just picking up the idle 100rpm stops the rattle/knock on tickover (Im referring to the timming chain noises and lazy tensioners here). G

Hi Gary, the only part of the system that the oil pressure effects (in terms of cylinder scoring) would be the oil spray jet effect on the under piston temperature and cylinder lubrication - but I don't think 100 rpm would make enough difference to that. But of course just pulling away more gently before ragging the car (or even just revving it up a few times before setting off) achieves a lot more with fresh oil everywhere and time for the coolant to circulate and the thermostat to re-set and keep the engine at the right temperatures. Baz

gtphile said: The turbo and GT3 engines do run an intermediate shaft, but it uses white bearings, running in oil, I beleive that was what the guy above you was suggesting converting too. That was my point yes. I know it has the IMS too, only direct driven with gears instead of a duplex chain. But as I see, Baz has answered it for me. It would require a pressurised feed instead of splash lubrication.

Does the X51 suffer the same problem? 996.2 3.6

"Does the X51 suffer the same problem? 996.2 3.6" From personal experience yes, when i bought mine i thought the extra cooling would help but still ended up with scored bores. The mileage was 58k.

Yes the problem being that regardless of the additional radiator the engine will still run at all the same temperatures controlled by the thermostat - without lowering the temperature of the thermostat the only advantage of the third radiator is in instances when the thermostat is fully open yet the system cannot cool the engine enough with two radiators. The assumption is that someone buying an X51 will be likely to drive it faster than a std car - hence the need for extra cooling capacity in hot conditions. Withough lowering the coolant temperature below that of the std thermostat - all the same conditions at the piston and cylinder face remain just the same. Baz

"So – put simply – I think that if the owner of one of these models – on a spirited drive - could not then resist the temptation to floor the car away from standstill (at say lights or junctions) - then I think we could have the worst possible scenario for piston/cylinder scoring at that precise moment." I have to admit - this sounds right to me. I am, unfortunately, someone who's recently experienced this in my 2011 Cayman S. I had the TPS high pressure turbo kit installed, and the car is just a wonderful thing of beauty. One day on the way home from work I got into just such a situation as described above, right down to the punch-launch from a red light. The car "gave up" on that acceleration, and I limped home, humiliated at having been dusted. The next morning on the way to work it failed altogether and I had to pull over and have it towed to my shop. I'm hoping it will be ready to pick up tomorrow - they replaced my 84k mile engine with a 36k mile one, so I'm trying to tell myself that this wicked expense is tantamount to buying a large chunk of the car's life back. Needless to say, I will be much more circumspect about playing with the turbo in the future - I'll probably completely give up my "from standstill" launches and push the edges only when I'm in a thoroughly warmed up condition. It was an absolutely heartbreaking experience that I never want to endure again (nor can afford to, for a few years at least). Thanks for the superb write-up, Hartec.

So, in hopes of avoiding this problem in the future I do want to consider that lower-temp thermostat, and also am interested in making the best "oil decision." I've simply followed manufacturer's recommendation on the oil in the past. But I live in Houston, Texas, so it never gets "up north cold" here - I'd be very happy to hear any advice on how that should affect my oil choice. Thanks, Kip PS: Love the deep technical talk here. I'm not a car expert myself, but I am an engineer and PhD, so I'm able to follow along pretty well.

Are you saying your 6 years old gen2 engine just gave up on 87k mile?

Well, it had a failure. This particular failure, based on the shop diagnosis, and my driving behavior just prior fits the OP's suggested "scenario" about as closely as it possibly could. Bore scoring, etc.

I've just read this old thread start to finish - some very useful information for a 996 owner - many thanks to Baz @ Hartech for taking the time to pass on his findings and advice. One other point to add, I recently changed the engine oil on my 2003 996 C4 from 10w-40 grade to the slightly thicker Millers 10w-50 which Hartech recommend. I did see a noticeable increase in engine oil pressure when the revs dropped to idle with a hot engine, which is I would think a very good thing considering the failure mode/root causes discussed by Baz.

Especially good of Baz to disseminate such good info, when it is effectively doing himself out of business. I value his advice very highly and am extremely grateful for it. I use an LTT and Millers Nanodrive10W-60 changed annually at most, for peace of mind, based on his advice posted online.

I know this thread is YEARS old at this point, but the info provided by Baz is some of the best I have ever read on this site. I'm in the 997 market at the moment and have found a few very nice C2Ss and I am going to look at one at the weekend. This thread is a goldmine of info. Cheers Baz and Hartech

I agree, there were times when Baz really had to argue to make his point ... now something commonly understood when Porsche were denying any involvement ??

churny said: "Does the X51 suffer the same problem? 996.2 3.6" From personal experience yes, when i bought mine i thought the extra cooling would help but still ended up with scored bores. The mileage was 58k. OK, so 15 year old post. But speaking to my Porsche specialist and he just said he has just seen his 4th 991 with bore score (or whatever it is but similar) and the same thing from all four is the fact all of them had the X51 option fitted. Shame Baz is no longer posting, would love to hear his thoughts on this.

Ed.Neumann said: OK, so 15 year old post. But speaking to my Porsche specialist and he just said he has just seen his 4th 991 with bore score (or whatever it is but similar) and the same thing from all four is the fact all of them had the X51 option fitted. Shame Baz is no longer posting, would love to hear his thoughts on this. He's commented on the 996/997 X51Powerkit engine option previously. His words were something along the lines of : "X51 not immune, on the contrary, percentage wise, we see as many if not more X51 failures (pro rata), than non-X51 failures.

Was always interesting hearing from Baz. I take it you mean the 991.1? I don’t think any model is safe from bore scoring, with reports of 997.2 suffering although mainly the S. I do often wonder with the way some of these cars are used may be a contributing factor. Short trips and not being regularly used, not getting oil up to temperature before taking engine over 4k, not enough oil changes etc One of things I always did on my 981GT4 2-3 miles from home I use to put in sport mode for the lower temperatures to help cool down as engines run hot for emissions which can’t be helping