Center rad + 160F thermostat stress test results with pics

Yesterday I had to go out in the afternoon for some errands. It was a hot day, and the car was running great so I decided to keep track of the temp during the trip and snap some pics of the results. I put the thermo and center rad in back in May, and haven't stressed the car much since then. I also cleaned the rads, and the AC condensers at the time of installation. When I left the house the OAT 100F, 41%RH, 29.96"Hg. As I got into the city, temp came up to 102 by the bank thermometer(usually accurate). First pic, leaving town, where the thermo started to open. No AC use Second pic, Cruising down the fwy out in the country. No AC use Third pic, in town stop and go. This is about the hottest it got during the trip, AC on high, fans running. Fourth pic, almost to destination, about 25 min driving in town, stop and go, full AC, OAT 103. On the way home, the temp dropped back to the left of the '8' slowly, and stayed there for the remainder of the trip. I don't have a before to share, but one trip in early May with temps in the mid 90s similar traffic, the needle would be over to the right of the little bulb icon, and move near the gauge tick to the right of the '0' before coming down when moving. I didn't like that, and had some concerns about driving in Aug in TX. Some of the gains can be attributed to rad and condenser cleaning certainly, but I'm sure the rad and thermo have provided great benefits to engine longevity. Things I've mentioned before, but bear repeating. I love the cooler AC at the vents. It's a noticable change. The cooling fans come on less, or run at lower speed after the rad and thermo change. Gained a little improvement in oil pressure, and it's even better now that I changed to 5W-40. For anyone in hot climates I would encourage these two mods when cleaning rads.

very interesting. With my low temperature LN thermostat I have noticed no changes in the dash needle, it goes as high as to the right of the "0" on the "180". I have yet to clean my radiators since I owned my car.

My normal temp in my stock 2000, the needle is between the 8 and the 0 no matter how hot it is. The only time it ever goes higher is in bumper to bumper traffic.

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Stock '02 here, seems to always be between the 8 and 0, maybe a hair further to the right if in heavy traffic on a hot day but not usually, and NEVER to the right of the 0. Cleaned my radiators a couple of years ago, there wasn't a huge amount of stuff in there but probably still worth doing as it's easy enough and sort of interesting to see how it's built.

I never understood the lower temp thermostat install. I lived in Dallas for 4 years and I used to run the **** out of my n/a 996 and then idle in traffic and never got past the 0 of 180. I could see using one if you track the car maybe though.

^ By the time you've run the **** out of the car on any given day, there is no benefit to be derived from a low-temp t-stat. I ran my 996 from sea level to 8,400 feet in ~87-degree weather yesterday... with the AC on. As long as your radiators are clean and functioning, the 996 doesn't overheat. Same drive in the same weather in my Corvette, I run the heater on full blast the whole way up. It sucks.

There's lots of 996 mods I don't understand, so I get that. My op-ed is no better and likely worse than a lot of others. Heat kills, and the 996 is particularly sensitive to thermal induced failures. So - about $400 total to help avoid a $16-20k problem. I considered it a good investment while I had the coolant out, and the rads removed. If you want to keep your rads and thermostat - you can keep your rads and thermostat. This was the hottest I could possibly get it. This was the greatest stress I could put on the cooling system, and I like that it barely got above 180F. Better for the heads, oil, AC, bearings, etc.

The smarter brains at Hartech recommend it. Good enough for me. Anecdotal "I never saw anything wrong temperature wise in the 3 years I owned my car" are fairly useless statements. Based that logic, there are no weak points on the car..we just keep them too long.... And if I could easily afford to only own a car never out of warranty, I would.

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You really do not know what the coolant temperature was under your test conditions. You should have used an OBD2 code reader/data viewer to view the coolant temperature in real time.

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The list of things I should have, and should do is - endless. As for what I do know at this point is the temp of the coolant sensed at the engine coolant sensor is a good 15F and maybe a bit more than it was when I bought the car. I also know the oil pressure has seen a slight but noticeable rise(due to lower temp), the AC runs the fans less when on, and I seem, but cannot state with accuracy that my fuel economy is better. I attribute this to a slightly lower adiabatic temp in the intake allowing for a slightly better intake charge. But again - this is not well quantified.

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I agree. Once the car is up to operating temp and the thermostat is open, what difference does it make what t-stat is in there? Even so, I just put a low temp thermostat into my track Boxste' because I am having some overheating issues with it. I figure if it opens at a lower temp quicker, it may reduce heat build-up. But, this may be pure fantasy.

I'm about to install a center radiator in my '99 C4. AFAIK it's got a 180 degree thermostat in it. The standard full operating temp is the temp needle on the right side of the 8 in 180. In hot weather with AC on in traffic, the needle climbs to the left side/half of the 0 (never to center). It's never gotten past this point since I've been driving it (since Oct '14). Once I get the center rad mounted up and start driving the car again, I'll revisit this thread and post the difference...

Read the article by Hartech. According to them, 3.4L do not have cooling issues; 3.6 and 3.8 do have, due to a change to the headgasket design then implemented. Another note on the displayed temperature is that what you see is not what the engine experiences, especially on the 3.6&3.8...so while the temperature seems rocksteady, it actually is not.... Volkert

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Gonna hafta respectfully disagree with ya there sparky. The job of any thermostat is to regulate the flow of the coolant around the jacket of the engine. In some case, as I posted in this thread, I stressed the car to it's maximum, indicating that the t-stat in my case was fully open, and flow was only interrupted by the button and flange. But - full flow of the coolant isn't always or even often the case. In many case, particularly in cold weather ops the t-stat isn't fully open. In some northern countries, the t-stat may remain closed all the way, as the thermal delta between the engine and the surrounding air is enough to keep the engine from overheating. Ever see a truck, or even a car with a piece of cardboard over the rad? There ya go. Too much dissipation to warm the coolant. So what this means is that the cooling system will operate the engine at the temp of the t-stat(which I showed with pics above in the most stressed case). Because I added cooling capacity to the system, I could induce my t-stat to go from fully open to regulated state. This was also confirmed by noting the fans cycling as motion was enough to dissipate the heat just by normal air flow. Now, 'heat' in the engine can go from ~1400F at the exhaust valve and seat, to likely below 180F at the base of the sump plate. So, measuring the temp of the 'engine' is a relative thing, and that's why I said that the temp sensed at the coolant sensor in the engine responded favorably. Of course - the temp of the exhaust valve and seat prolly didn't go down hardly at all. But, here's the key for me. My oil temp went down, as I noted on the increased oil pressure after installing the t-stat and rad. The coolant temp in the engine went down, my fuel economy increased slightly indicating improvements in reduction of adiabatic heat loading. All these taken together tells me I'm comfy saying that the stress on the metals in 'the engine' have been reduced. Piston faces, cylinder liners, rod journals, crank journals, cam chains, guides, bearings are all seeing lower temps due to lower coolant circulation temps and lower oil temps. The thermal loads on the life fluids of the engine are being carried away sooner(or at a lower temp) than if I had the 183F t-stat in there. That's my op-ed, and I stand by it. Lower temps are good, regulating at 160F is better for the whole engine(exh valve notwithstanding) rather than running it at 183F with the t-stat in full exchange mode, and reliance on the fans to keep it from overheating.

^^^^ Very Macster-like, but I'm waiting for the REAL Macster to chime in with his essay.

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Hmmmm, one of us - should feel insulted. Not sure which though!

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According the Hartech and Jake Raby ,the problem reduced by installing a LTT is cylinder deformation . The temperature spikes that cause cylinder deformation are not indicated by a high coolant temp gauge reading - because it does not measure the temp of the critical part of the cylinder . The problem IIRC is lack of adequate flow around the vulnerable area. Once the OEM Tstat is partially closed ,flow to the vulnerable area (Bank 2 thrust face) is inadequate and cylinder overheating occurs - but is not measured by the stock instruments. The LTT stays open longer and reduces this issue. The next stage is to modify flow in the coolant console and the cylinder head gasket and water jackets. If cylinder deformation is the concern, the stock coolant temperature gauge in the instrument cluster is not a direct measure of the problem.It is barely an indirect measure. And driver anecdotes are obviously not a substitute for cylinder temperature measurements. If coolant boiling is the problem ,that is a different discussion. A simple way to measure bore thrust face temps on 4 ,5 & 6 would help.Anything closer to this area than the coolant temp sensor would help. Just follow the coolant temp flow chart- the coolant sensor is a long way in the wrong direction from the critical area.

We bought a boat load of the low temp t'stat's and need to move a few out the door. https://rennpart.com/product/thermos...removed_item=1 while you're down there check to make sure your water pump isn't a duck call, we're glad we replaced this water pump on our 986. There was no reason to believe we needed to replace it until we pulled it off

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IIRC, both of those individuals found some design issues with the size of the coolant passages in various parts of the head casting on later engines, 3.6L? Where the coolant flows were restricted due to the same size holes being downstream from the flow direction caused some cyl to be poorly served by the coolant. But - I admit it's been a while since I read it. As for the measurement of the entire system, unless we instrument every passage, every bottleneck, and every inlet/outlet pair, all I can say is the overall temp of the engine went down. If that means I had a hot spot in one cyl area(but I don't because I'm a 3.4), then reducing the aggregate of those instrumented collection of points means I had a reduction over all. My memory of thermodynamics from school is 30 years old, but I do believe the thermal xfer parameters between two areas of different temps still holds. So, If the coolant in the nearby passage is lowered, it will offer a thermal path for exchange to a hotter area. After all, that's the whole idea behind temp extraction of the entire cooling system. I am unwilling to go to the expense of removing the engine, removing the heads, and grinding out the coolant passages for greater flow. So, I added a rad, and a lower t-stat as a reasonable low tech, low cost, modest gain alternative.

It is not that hard. The critical factor is the temperature of the thrust face of Bank 2. An aftermarket cylinder head temp sensor + gauge for Bank 2 would be a huge step in the right direction.Just bolt on the ring terminal in the best convenient location. http://www.ebay.com/itm/CHT-Cylinder...1UrtHM&vxp=mtr http://www.autometer.com/cylinder-he...rmocouple.html http://www.ebay.com/itm/CYLINDER-HEA...4AAOSwPhdVNzLe

I hope you weren't driving when you took those pics. If so, you are in violation of CA Vehicle code and could get a cell phone usage while driving ticket

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I was driving. the pics were taken west of Fort Worth TX, and then in town. The Republic of Texas does not recognize/enforce CA vehicle codes. (*don't try this at home, pro driver closed course, YMMV, all sales final, contents have settled and may cause **** leakage*)

To the other 99% of you who aren't having any problems, enjoy your car. I once was driving my race car back from the track (old school), it was night, no dash lights, and as I passed an overhead street light I saw that my engine temp was at full max. I have no idea how long it had been there but I immediately pulled over. The pully that drove the water pump had failed...it split and took the belt with it. I let the engine cool down, it was bone dry so I added some coolant and made it to an all night gas station. The next day it was flat bedded to the guy who built it. Bottom line, no damage. No warped head, etc. This was on a 1958 Alfa Spider Veloce...1290cc, 8000 rpm red lilne every lap every gear every race. We put on a new aluminium pully, filled up the coolant and I continued to race it for two more years. I have to believe that a Porsche that is 40+ years newer has enough engineering expertise invested in it to allow it to drive normally without thermal destruction.

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LOL

To the other 99% who are not having a problem, enjoy driving your car. Many years ago I was driving my race car home from the track (old school) and without dash lights it wasn't until I passed under a freeway overpass that I had light to glance at my gauges. The temp was at the max...pegged all the way. I immediately pulled over. The pully driving the water pump had split, taking the belt with it. The engine was ticking like a bomb and bone dry. I let it cool, put in some fluid and made it to an all night gas station. The next day it was flatbedded to the shop. There was zero damage to the motor. No warped head, etc. We gave it a new aluminium pully, refilled the radiator, and I raced the car for another two years. This was vintage racing and we could not used normal coolant, only water. The car was a 1958 Alfa Spider Veloce 1200 cc, 8000 rpm red line, which it did in every gear, every lap, every race. I have to belive that a 40+ year newer Porsche is built with enough reserve strength and capacity to handle day to day driving, even in 100 degree weather. And I have to believe that the engineers who design and build these cars, test them well enough to discover any thermal issues before they sell them to us.

I never had any problem with the cooling system on my car prior to this alteration. It operated nominally. I just made the nominal better. Finally, I must say I'm flummoxed with all the picking of nits in this thread. I was hoping it would be used as a simple benchmark for what could be accomplished by making a mod which I found quite beneficial. Rather, it's been a list of 'yeah - well, GFY, I don't need it' theme of comments. All in all, a bit disappointing, and why I haven't offered any more observations on methods to improve.

" it's been a list of 'yeah - well, GFY, I don't need it' theme of comments. All in all, a bit disappointing, and why I haven't offered any more observations on methods to improve. " Sad, I agree when those of us who try hard to share and discuss technical issues get shouted down by the peanut gallery. On one other Forum I participate in, the Mod is ruthless and just deletes the posts you mention. The 'contributors' of the petty sarcasm and dismissive comments soon move on .The result is a very useful resource that I gladly support. To be clear, your mod 1. did no harm 2. was inexpensive 3. follows expert conventional wisdom 4. was interesting and helpful. Few other posts rose to that standard. So thank you for Posting.

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I disagree. So far, it's been a good thread with various opinions. Tons of people recommend doing the low-temp T-stat swap, but I've also seen arguments against it, and also discussions that it has limited or no value. I think its a topic worthy of discussion from all points of view. Since I put the low-temp thermostat in my Boxste' it has definitely been running cooler. Never even gets above the 180 mark during highway driving. On the track, it's bumping 225 or so. But, I changed out my water pump and did a coolant flush at the same time the t-stat was replaced, so too many variables.

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Bear in mind that the center rad doesn't have a fan behind it. I see a decent temp reduction at highway speeds, virtually no effect otherwise.

In the 3.4 engines/VarioCam engines the head gaskets had different size openings for the coolant passage to each head and there are left and right side gaskets. The theory is that there are smaller openings for the cylinders toward the rear of the car which are closer to the water pump and the temperature of the coolant is lower. As you move toward the front of the car the openings are larger, there are three different sizes, so that more coolant flows. When they went to the 3.6/3.8 VarioCamPlus engines the head gaskets have the same size opening for each coolant passage and the left and right side gaskets are the same. Some have conjectured that this was done as a cost savings measure. This may the the reason that the 3.6/3.8 engines are more problematic. Also, remember that the temperature sensor that measures the coolant temperature for the gauge is located near the water pump in a housing of the front of the engine as viewed from the rear of the car. If you look at the coolant flow of the system the coolant having passed through the engine, so at it's highest temperature, then flows to the front of the car, through the radiators where it is cooled to it's lowest temperature, than back to the rear of the car and the water pump. So the coolant where the temperature is measured is at its lowest temperature, much lower than the coolant coming out of the engine. So fi the temp gauge is showing 80 degrees this is after the coolant has passed through the radiators and the temperature of the coolant coming out of the engine is much higher. So having a low temp t-stat allows the coolant to start flowing at a lower temp at the temp sensor where the coolant is at a cooled temp which is probably a good thing.

Excellent Cliff Notes for those who do not read Baz.Thank you. Any comment on coolant temperature based on the gauge is probably confused . The stock location for the CTS does not read the hottest part of the coolant and causes under-reading at the gauge. It also fails to read temperature spikes from the hottest part of the engine. This makes the entire cooling system slow to respond to these spikes .The spikes can be severe enough and the coolant flow/volume poor enough to cause localized boiling.see links below for more. The engine bay temperature sensor is also poorly located but that is easy to relocate to fix the problem. By comparison, moving the CTS is not practical. Neither is modifying the coolant console,gasket holes etc. So fitting a low temp T'stat is a compromise.Hartech ,Raby and others are well aware of this and do many such mods in their engine builds. For those with a technical interest in this subject ,it is easy to acquire better data.The cylinder head temp sensor kits linked previously can be bolted on to several different locations of the crankcase so you can see changes in real time. A 10mm ring terminal on the kit makes it easy to move around and plot the variations. None of this is new - for example: http://www.pistonheads.com/gassing/topic.asp?t=988167 http://www.pistonheads.com/gassing/t...t=1052310&i=60 "All our tests on the 996 versions show the gauge moving but reading low after 80 deg.C, The biggest problem I can see occurs when the engine is driven spiritedly. At that moment the cylinders will imediately get hotter and conduct that heat to the cylinder block and the coolant in it - but in that block the amount of coolant is small (compared to the amount passing through the cylinder head) and the cylinder head is no where near as quick to conduct the heat outwards and to the coolant (which is flowing through it in large volumes). So the small amount of hotter cylinder block coolant mixes back with the larger amount of cylinder head coolant (which is still cool) and passes at little increased temperature to the radiators - which therefore have a marginal affect on the temperature drop (being a function of the temperature differece which has been diluted by the mixing ratio). It then passes back to the engine thermostat which hardly notices the difference and in any case is designed to react slowly - and back round the engine again. While all this is going on the temperature between the cylinder wall and the piston has increased significantly and with it the oil separating the two gets thinner and does not provide the support it should (while the coating on the pistons may get too hot). Eventually it all settles down to a constant temperature again until the driving style changes. If you compare this with more traditional engine design, all the coolant frst goes into the block and cools it quickly first - then it passes through the head (so even if the cylinder block temperature has increased - the head raises that temp little more than before for a period of time) and the result then hits the thermostat (which sees the higher temperature and opens more) and then it almost imediately goes into the radiator. If you then fit a higher temperature thermostat (to help run the engine with reduced emissions) and cheat the dashboard reading (to avoid upsetting owners) - you get the scenario in full. Without re-machining inside the engine - unless the thermostat is changed to reduce the temperature it opens at - there is nothing any other changes will do to influence the cooling rate of change inside the clinders - because that thermostat controls the flow rate and the balance of coolant flow inside the engine is unchanged. It has long been proven that for best power and longer life - a lower running temperature is better - but racing is not subject to emission controls (that could handicap a new model being allowed to enter some Countries - especially the USA) and hence to keep increasing performance and fuel consumption combined with lower emissions - engines for road cars are progressively being run hotter - for the first time in a long period of development of something quite different - and in my opinion - not every manufacturer has got the whole system thought out to enable their engines to maintain the level of life expectancy they used to enjoy (and may be that is impossible anyway!). Low temperature thermostats are now available from us @ �60.00 + Vat (fitted by customers at their risk) please contact us or your chosen specialist for a quote to do the whole job. Baz"

Anyone know if gas mileage changes with the low temp t-stat? Ill chime in my knowledge on this subject. The issue I see here with the standard temp t-stat is that it fully opens at over 210F, which means that the real temps are certainly higher. If folks are seeing the water temp gauge past the 0, you're well into 104C, about 219F, about the top of the spectrum for when the fans are on max and the flow of coolant is full. Which means that actual temps could be 5-10 or more at some places, maybe 230F. You now have very little cushion before you're engine is running "hot," The old Bruce Anderson temps guidelines being: 220 - ok 230 - warm 240 - hot 250 - too damn hot In an ideal world, you would even just want a t-stat to open sooner, you'd want the range of temps to be narrower, if possible, so you'd have the fans turn on a bit sooner.

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FWIW, with the factory T-stat my 2002 Boxster in 116F ambient temperature never had its coolant temperature go over 226F. Both fans were running -- on high -- but the coolant temperature went no higher. The engine was fine. (The coolant temperature has hit 226F since then in lower ambient temperature conditions. For instance in summer on mountain roads enjoying the drive if you know what I mean and I think you do I have observed -- using an OBD2 code reader/data viewer to monitor coolant temperature -- the coolant temperature again reach but never going above 226F.)

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Someone said: "Any comment on coolant temperature based on the gauge is probably confused." We only know what the gauge tells us. And that under-reads the temperature in the critical areas of the engine. "The engine was fine"- so what was the temperature of the coolant in Bank 2- where the overheating damage slowly occurs? Answer - no idea. Damage done - no idea but probably none detectable until the bores are measured.Hopefully none them Baz covers this issue in detail in the links provided. Jake has also made all these points and more directly with you in a previous Post. So I accept that you do not accept their data &/or their conclusions or recommendations. All I am doing is highlighting some of their work. I certainly would not offer a personal anecdote to refute their conclusions.