Best oil?

Hi Guys, I've noticed that most literature recomend a 0w40 or 5w40 oil for the 3.4 996. I was speaking to a chap from Hartec the other day about servicing costs and the oil they use, and he advised that for a a higher mileage engine 0w is too thin a base for the engine and a 10w base oil should be used? The car last had an oil service in March and has done aprox 4.5k since. I'm getting the service done in March again at either hartec or northway, but in the meantime I thought about dropping the oil until then (even though it's clean, again some people say bi annual is a good option to prolong engine life). With that in mind, what oil would you guys recommend? Mobil? Castrol? and 10w40? Thanks, Steve

oh sorry and fully or semi synth as I have read mixed views on this too. Thanks,

The Porsche Approved oils list is mainly 0W-40 and 5W-40, and all are fully synthetic. IMO a 0W-40 is too thin for a higher mileage engine, and you will find most indies would recommend a 5W-40 or 10W-40. The approved list is in the member's only 996 Technical Articles section of the forum (which you won't be able too see) but if you would like a copy, drop me an email and I'll attach it to a reply. I used Fuchs Titan Supersyn 5W-40 in my C2, and changed it every 6000 miles, but I would go with whatever Hartech or Northway recommend if you are taking it there next time.

Hartech are probably the most technically knowledgeable people about Porsche engines so I would go with what they recommend (which will be 10W-40 semi synthetic - which Baz Hartech has good reasons for choosing) as they really do know what they are talking about - wish they were nearer to the south of England !! I use 5W-40 fully synthetic in my 996 Tutbo as it has only done 32K so far but I do change it every six months.

Thanks Richard and Eddie, I'll be joining up soon And thanks for the offer of sending over the list.

Steve, Be aware that the 0W or 10W part of the multigrade rating represents the viscosity only when the oil (engine) is cold, so once the engine is warm the viscosity for both will be the same at 40 (the upper viscosity is measured at 100 deg C). So, the 0W-40 is only thinner than a 10W-40 whilst the engine is getting up to operating temperature, and will in theory be able to get around the oil ways better whilst this is happening... But may also be able to get past your valve seals and piston rings easier! Tony

Thanks. My understanding with a multigrade oil is that the lower rating means just as you have said, it is thinner when it is cold so it can circulate around the engine quicker, however, it takes longer to get to the viscosity of the 40 rating, as the base is thinner, so it's a bit of a trade off. A few places I have spoken to say that whilst a 0w40 should be the same as a 10w40 at higher temperatures, in reality the base oil is thinner so it will be somewhat thinner even at temperature. I've always used 5w40 fully synthetic in lower mileage engines, and 10w40 semi in older car engines, there is no real science behined this, just than my father was an old school mechanic and this was what I grew up with I noticed that everywhere states 0w or 5w40 regardless of mileage on these, so when I was told 10w40 I thought I would ask what you guys use. I think I'll go with the 10w40 that hartec recomended for now and see how we go until the next service. Thanks for your comments.

A long discussion on this topic has been going on with regards probs with 997 engines at the moment on Pistonheads and one of the points that Baz Hart makes is ----"Yup I did understand how the oil viscosity range works and that they are basically saying that at normal running temperatures it should be as good as a 40 grade whether it is a 0-40 or 10-40 or 5-40 but this depends on that running temperature and without doubt as oil gets hotter the viscosity falls. In my experience that is not the case by just simply seeing it drip or pour when hot and anyway - it seems very thin and the 10-40 etc seems thicker - but anyway I think we are missing a rather obvious point - that runs throughout this posting. It is always a mistake when people with experience find out something from experience - to just rubbish what they found out by some technical argument that appears to appose it. People don't run engines with something less good than something else - they always want the best and if someone finds out that one grade of oil gives better performance than another - they don't have any unlterior motive for suggesting that and have nothing to gain from doing so - but failure if they are wrong. I really get anoyed when people who have not experimented with different oils (and the same applies to lots of different technical issues) argue against someone who has on the grounds of some accademic empirical rule they believe in but have never tested. I have found (and so has any successful development engineer anywhere involved in racing or engines) that if experience shows up a trend - you absolutely must take note of it and act accordingly - even if you don't understand it yet - because there is always an explanation that eventually emerges. It is OK to discuss and even dissagree on what might be the reason behind all sorts of phenomenon but never doubt that the phenomeon exists or consider that the solution or improvement found by several people was actually some blind mindless mistake and that they actually made things worse but didnt't notice it. Right throughout the history of the problems with these engines we have quickly and successfully found the right solutions. They were based on our technical conclusions that we often openly convey to others. However the conclusions may be wrong or misguided in some cases - but if the solutions actually work - it doesn't matter if the reasoning was a bit out (not that I think it was) as much as the solutions working (which they all do). Debate about the reasons behind failures is IMHO good for everyone and sometimes throws up new issues that are of interest - but more often simply finds others who found the same problem and solution worked (as in this case). Dont forget that the running oil pressure is limited by the oil pressure relief valve - so the running oil pressure may well be the same on the guage - whatever oil is in the engine - but the oil has to travel through hot castings to get to the area it lubricates and by then (like typically when trapped between a piston and cylinder wall that is hotter than say some other engine) will be thinner and a thicker oil may well work better there even if the oil pressure on the guage is the same. If (as I suspect/believe) the temperature of the coolant coming out of the cylinders is hotter than the greater amount coming out of the heads - before it mixes together again - then if (as I suspect) the cylinders are running hotter than normal (or in more tradditional engines) and especially since the lower half of the cylinder casting is now in contact with crankcase oil (which is taking heat from it) then it is possible that the oil running temperature is hotter than the temperature that the comparative viscosity was taken to list the range for the oil under typical conditions - or in critical parts of the engine. Furthermore - if we compare the 944 turbo (say) with the 996 - the lower cylinder recieves the coldest coolant directly in the 944 wheras the 996 lower cylinder is not cooled at all by the coolant and the upper cylinder that is cooled by it - receives only a fraction of the amount of coolant the 944 received = the lower cylinder casting must be running hotter in a 996/7 than a 944 and the oil in between the piston and the cylinder must be hotter and therefore thinner. If this is the case then using a higher viscosity oil simply makes the rating between the hotter piston to cylinder wall area - the same as it might have been with a lower viscosity oil in an engine running cooler in that area. Put simply - the oil might indeed be thinner in parts of this engine and therefore a lower viscosity because the engine is generally running hotter - especially in some areas that oil is in contact with or used as the alternative cooling agent."---- Although I do not understand the more technical side of oil I do think that when an expert in Porsche engine rebuilds who is helping many people sort out major problems with 996 / 997 engines states that he recommends a higher grade of oil then people should at least listen to his points.

I've been doing a little research and taking into account the above as well - here is my thought: The testing involved for the oil to obtain the 40 rating or whichever comes after the winter rating is aprox 100 degrees C (as I understand it). This should in theory mean that most engines fall within this scale and as such the oil should be thick enough at high temperatures, however I can see the argument that a thinner base oil is in theory, still a thinner oil, and certainly to start with and may not fully change viscosity until higher up the temperature scale. IE. If tested at 100 degrees C, then what is to say at which point the change in state is at say a normal 'hot' or running temperature of 85?, or indeed 50 degrees C while the engine is warming? With that in mind, if the middle-point of the oil or the point at which the normal operating temperature of the 996 engine is reached is below the temperature tested to obtain the rating, then we will likely be assured of running thinner oil than that of the actual rating at that specific temperature (100 deg C). Taking into account a higher mileage engine with no doubt some internal wear on the surfaces etc, we should (for those of use with higher mileage engines) indeed be running a thicker oil. I'm obviously not an expert as you can tell, and anyone new coming to the forum and reading this later should know this is pure speculation, but in my eyes it seems to make a little more sense now, therefore as recommended by Baz, 10w40 it is Thanks for your input as usual guys.

I love it when this subject comes up periodically there is probably more bull circulating on this subject than anything else,and also more subjective opinions and more anecdotal "evidence" FWIW I use mobil 1 0w-40 and generally change it every 5000-6000 miles It is porsches recommended oil now I do understand some people like conspiracy theories but Porsche are first and foremost a superb engineering company and they run their engines to destruction and they use these oils,you are very unlikley to go wrong using what Porsche suggest.I however do believe in increasing the changing frequency,as oil is so cheap annd it is possibly the most important component in the engine.One can argue about the viscosity and it importance but surely life is to short. I have always worked on the idea that a 0w oil is less viscous at low temp and much closer to its operating viscosity therefore it can do its job from the get go,which is where most mechanical wear occurs.In an engine like the turbo depending on how it is driven and journey cycles this usually means greater oil use.Oil also has so many other jobs it is also now full on science.If you are interested https://www.amsoil.com/lit/g52.pdf http://themotoroilsite.com/phpbb/ the above website will also point you to the motor oil bible there is also another guy who posts regulalry in the uk called the oil man Happy reading I'm off to the pub

I didn't want to get into a debate about oil as it very quickly gets very silly however you might change your mind if you become one of the few people who suffer an engine failure (hopefully not) and get no help from Porsche. Then you might need the services of one of the experts in this field (Hartech, Autofarm) all of whom will tell you that you would have been better with a higher grade oil - film strength is the most important thing in a cylinder to piston face joint/gap and the higher the load the higher that needs to be to keep the metal parts apart! and too hot is bad news if you are using a "thin" oil.

One important point about oil which has not been highlighted in this thread so far is that oil is there not just to lubricate but also to cool and both of these functions are of equal importance. The observations made about oil temps in a 997 engine may actually be as Porsche intended - i.e. they are using oil to cool the engine moreso than in a 944 engine - using the 944 engine as a benchmark may not be a valid comparison, the game has moved on since then. If you go to an oil viscosity that is too thick then the flow rate of the oil is reduced and therefore the properties of the oil may be compromised. Oil pressure is a red herring - the most important thing about oil is its flow rate. Who knows what Porsche engineers intended when designing the engine, but I do know that by just experimenting with thicker grades of oil is just at dangerous as experimenting with thinner grades of oil. The thing that modern fully synthetic oils bring to the party is that they maintain their properties to higher temperatures which allows them to be run hotter and still provide adequate lubrication and Porsche may be exploiting this property moreso in the 997 engine design. None of us were on the Porsche engine design team so my feeling is that you should stick with the Porsche recommended viscosity (which will cover a range of viscosities and not just 0w40) and you should be fine at any mileage. There are alot of untruths, assumptions and incorrect 'facts' floating around about this subject, and I don't know the answer and neither do most if not all of the 'specialists' out there (as 10 specialists their opinion and you'll get 10 different answers all based on their 'experiences'), so i'd prefer to use the manufacturers recommendations - unless I was using the car for purposes outside of their assumptions e.g. if you're racing the car or using it hard on regular trackdays.

It would seem then, that this subject has no definitve answer, whilst I understand that porsche recomends X oil grading for a purpose for engines from the factory, I doubt they bench test the engines anywhere near to a high mileage road engine (although I could be wrong?). Take into account also that bench testing is totally different to driving a real car in real conditions, I doubt that they can say what is best for sure for any particular high mileage engine without having stripped high mileage engines down to see how they age. Hartec is recomending 10w40, there is no 10w40 on the approved list that I have read, the highest is 5w40. I was going to take Gav's word who I spoke to at Hartec over the OPC recomended rating as he has likely seen much more older, higher mileage engines both inside and out than an OPC who would mainly see shiney new motors. I of course, don't want to 'trash' my engine and I want to do whatever is in it's best interest regardless of cost or where I source the oil from, but it's just making sure that I get the best for this particular point in the motor's life. I'd be interested in hearing from those who have used 10w40 and their experiences with running this oil. Thanks, Steve

Porsche recommend 5W oil as a maximum for 996 engines onwards due to 10W being too thick for the Variocam system... 10W is OK for earlier aircooled engines They also recommend fully synthetic oils only I believe - I cannot understand why so many Indy's recommend a semi-synthetic, the only advantage I can see is price. A fully synthetic oil will stay in grade much longer than any non / semi synthetic oil Porsche obviously test their engines to high milage using the correct oils that they recommend, but I cannot imagine that they run the engines on "lesser" oils just to find out what happens.... Pete