Choosing a low temp thermostat

I posted a thread before and somehow still can't see it so this one might be a duplicate. From the list of thermostats in Pelican parts page, which one is the 'correct' low temp thermostat. Porsche 996 Cooling System Miscellaneous - Page 1 As can be seen there are at least 3 brands (Wahler, LNE and MotoRad), and they vary in prices. If they are fundamentally the same, why would I get the most expensive one? The Wahler one has this "Water Thermostat, Low Temperature (begins opening at 160 deg F) with Cover and Gasket, 996 Carrera 2/4 (1999-04) Brand: Wahler" Thanks for your help!!

I'm on a similar learning curve with a 996 I just purchased. From what I read the 160 degree is the right temp for use. The LNE thermostat I think needs extra parts associated with the install vs a straight replacement. Have a read at the LN Engineering website and I'd appreciate your interpretation. I am in the process of rebuilding the motor and will probably install a new 160 degree thermostat that drops right in.

Yes I was talking about the low temp ones (160 degree). You can reuse the housing but will need to replace the gasket. I think LN's comes with the housing, hence the higher price. You don't need the 'tool' to change the thermostat. Use the cap of your shaving cream can. Gasket is about $5. However if you see on the page from my link above there is one from Wahler ($70), LN (170) and MotoRad ($80-ish). The question is whether any three will do the job, or do I have to use LN's. LN says that their thermostat is made in Germany. I wonder whether it's just a Wahler or MotoRad?

According to post #9 by JFP, the LN thermostat is made by MotoRad. Service time for water pump and thermostat question - 986 Series (Boxster, Boxster S) - RennTech.org Forums

I'm curious - why are you going to a low temp thermostat? If you're under the impression that it will lower the running temperature of the coolant, you may be wrong. I was considering putting a low temp thermostat in my '01 996 which is in good condition and stock. But I was curious to see how much the temp would fall. As an experiment, I removed the stock thermostat which has the engine running at an indicated 185F. Without any thermostat? Yup, an indicated 185F. It turns out that the thermostat is usually only for warming the engine more quickly and is NOT the limiting factor of temp. The capacity of the cooling system is the limiting factor. May save yourself a lot of time and trouble by trying this test on your vehicle before popping big $$ for a low temp thermostat.

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Sorry, but your hypostasis is incorrect. First of all, the dash temp gauges in these cars are well known and documented to be woefully inaccurate and non linear; they are little more than an idiot light that moves. It is not unusual to see one indicating 180F when the engine is actually at 205-210F. Secondly, the thermostat, assuming it is functioning correctly, acts as a throttling mechanism that controls the minimum steady state operating temperature of the engine. As such, it controls the lowest temperature that the engine will run at. Dropping the coolant temps from their normal 205-210F levels to around 175F with a 160F stat significantly reduces the inherent hot spots in these engine's that typically lead to problems like cylinder head cracking. The cooler coolant temps also lower the oil temps nearly 25F, which results in a huge improvement in the oil's life expectancy and performance. Changing to a 160F stat is one of the cheapest significant modifications you can make to one of these engines.

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LN stat is clearly marked as made by MotoRad.

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Absolutely NOT true. The hot spots in cly's that causes failure modes has been found to have many causes, one major one being debris in coolant channels or poor casting issues. It has not been caused by someone using an OEM factory spec thermostat. If this were true EVERYONE with a factory OEM part would be sitting parked now including my high mileage STOCK 1999. The temperature levels that your engine thermostat opens up at are designed this way for specific reasons due matching the features of the car/engine such as if you have three rad's or are using a Tip or PDK etc. The engines all have a temperature specification that the coolant has to be at (within a + or -) and this relates to emissions and other engine related reasons. The 'belief' that lowering the coolant temperatures is *always* better is urban myth and 1980's thinking when talking about a well maintained engine with modern ECM's control units. Over cooling an engine (out of Porsche spec's) is a sure fire way to set off a CEL or damage the engine in the long term. There are good reasons for factory operating specifications for normal use vehicles.

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Sorry, but you are incorrect. The cylinder head cracking issue stems from the design of the head which features several restrictive passage's (easily seen if you have ever cut one apart). While debris from issues such as water pump wear do exacerbate the flow restriction further, the major fault is in the severe thermal loading on the castings that take place during normal engine operations, when some of these areas can be as much as 40F (or more) hotter than the general coolant temperature, and significantly hotter than the adjacent casting areas, which has been observed by more than one shop. With the OEM stat just beginning to open at 186F, and not being fully open until the coolant is well in excess of 205F, thermal imaging of the cylinder heads shows some pretty staggering heat differentials between these restricted areas and the adjacent castings, even on brand new heads on a brand new engine, where there is no chance of debris blockage. And coincidentally, these areas of high heat concentration are were many of the castings crack: Switching to a low temperature stat not only dramatically lowers the overall coolant temperature, but it also equally dramatically lowers the temperatures of the known hot spots in these heads, and brings them closer to that of the adjacent casting areas, reducing the physical stress on the castings caused by the otherwise high thermal loadings. As for a low temperature stat causing a CEL, that is complete nonsense. With literally hundreds of customers running one, some for nearly a decade, I have never seen a CEL that could be attributed to lowering the coolant temperatures. Add in the reams of UOA's collected over the years on the cars running the low temperature stats, and you notice that the oil in the engines with the lower coolant temperatures holds up longer (stays in grade) without any signs of increased water or fuel intrusion. The improvement in oil longevity has also be born out when we have had the opportunity to check the rod and crank bearings on engines that had run the 160F stat for long periods of time, both on the street and the track. And just as a by-the-by, Porsche uses the same type of low temperature stats as OEM components in their highest performance engines, the ones found in the GT2, GT3, and Turbo cars

So why doesn't Porsche provide a 160F v. 180F as the recommended thermostat? Also, since I live in Florida, the thermal limit of the cooling system may remain my constraining factor.

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Porsche does use 160F stats, but only in their "maximum effort" cars like the Turbo, GT2 and GT3, as well as their cup cars.

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Trust JFP, he knows what he's talking about here. I live in Florida too and installing a 160 thermo made a noticeable difference in my running temp with a negligible increase in warmup time. I also have a 3rd front radiator installed. This past weekend I did a PCA autocross and was running the car for well over an hour and pushing it hard on the track. Granted it was only in the low 70's outside but it was sunny too. My oil temp peaked no higher than 210-215 and kept dropping to just a hair under 200 between runs, which is where it typically runs now whenever I drive it. Previously it was typical to see temps in the 225-250 range. This is on an 05 C2S btw.

" Dropping the coolant temps from their normal 205-210F levels to around 175F with a 160F stat significantly reduces the inherent hot spots in these engine's that typically lead to problems like cylinder head cracking. The cooler coolant temps also lower the oil temps nearly 25F, which results in a huge improvement in the oil's life expectancy and performance." With all due respect to JFP (I've read many of his posts here, on RennTech and several other forums - he's clearly an accomplished and competent mechanic) and any others who believe this; While I believe that lower coolant temps reduce inherent hot spots, how does a Thermostat "drop" the coolant temps. in an engine? Please no nasty/smarmy/flaming type replies. If someone feels like they have to "stick up" for the low temp. T-stat, please try to stick to facts and/or data to back up your argument/theory.

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The thermostat controls the minimum operating temps the engine sees, not unlike the thermostat on the heating system of your house. Can the car's cooling system get hotter when it is stuck in heavy traffic? Yes, but once moving again, it will cool back down to the lower steady state operating temperature set by the thermostat. By starting from a lower minimum temp, and returning to it when air flow over the cooling system allows, both coolant and oil temperature's are reduced, and any inherent "hot spots" caused by the mechanical design of the engine castings are running cooler.

"By starting from a lower minimum temp, and returning to it when air flow over the cooling system allows, both coolant and oil temperature's are reduced, and any inherent "hot spots" caused by the mechanical design of the engine castings are running cooler." Ah... So you're saying that due to the T-stat opening at 160 degrees, the block and oil temps NEVER reach the higher temps that they would reach with the 180 degree t-stat - therefore lowering the overall operating temp. of the motor ? This seems to make sense - much more so, than the T-stat "controlling" the coolant temperature. Thanks for the reply

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"... NEVER reach the higher temps that they would reach with the 180 degree t-stat ..." Not so. Although the thermostat sets the minimum operating temperature, the actual operating temperature is a function of the thermal efficiency of your cooling system. Might the somewhat divergent opinions be summarized as follows? - Cooler operating temperatures is likely to minimize head cracking. - Cooler operating temperatures is likely to result in improved performance. - Cooler operating temperatures will decrease heater efficiency. Yes, I know, but in some regions this is important. - The minimum operating temperature is established by the thermostat. - The actual operating temperature is a function of the thermal efficiency of the vehicle's cooling system. Above the constraint of thermostat temperature, as per above. - To achieve a significantly lower operating temperature, a lower temperature thermostat may be insufficient by itself. - Utilizing a lower temperature sensor to activate the radiator fans may reduce operating temperatures particularly in low speed applications, e.g. traffic. - Utilizing a bypass switch to activate the radiator fans may be desirable in performance applications. - The use of a third (center) radiator will improve the thermal efficiency of the cooling system. - If your temperature gauge is acting 'like an idiot light' it is likely that you have a problem in the sensor, gauge, or wiring that needs to be remedied. In my experience, these are reliable and yield repeatable results. Granted it is a single location measurement but this measure can be read with confidence. I return to my original statement - before investing in a low temp (i.e. 160F v. 185ish) thermostat, remove your thermostat and see how much (or little) the operating temperature falls. Then you can make an informed decision as to how to best invest your funds. BTW, I am running a 160F Motorad thermostat sourced from Pelican and I see a typical operating system reduction (Interstate speeds) of maybe 10deg off the stock thermostat. When participating in a track event, there is no change in peak operating temperature at all from the stock thermostat - both run about 200F. It may be my imagination, but I believe I see a slight increase in fuel economy as well - maybe an additional 1 mpg.

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Over the years, we have probably looked at the accuracy of the dash display in the 986, 996, 987, and 997 probably a dozen or more times across many cars, and have only every found a few that were even remotely accurate. The dash display is not only inaccurate, it is non linear in nature, further limiting its accuracy. This is particularly noticeable on cars equipped with aftermarket water temperature gauges which yield completely different results to the dash unit. It is not uncommon to have a car showing around 180F on the dash display actually reading 205-210F in the coolant jacket. And replacing the sensor, or even jumpering from a tested sensor to the dash display does not improve the results one iota. As such, we place little confidence in the reliability or repeatability of the dash display. Interestingly, dyno testing before and after switching to a 160F stat has also shown a slight mileage and very small but consistent power increase, believed to be the result of better engine efficiency at the lower operational temperatures.

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A common misconception. Your cooling system has the thermal transfer capacity to shed heat well in excess of what the engine can generate, other wise the engine would never cool down after becoming stuck in traffic; but the thermostat controls the actual steady state operating temperature. The simple fact that the operating temperature, moving from a factory 186F stat to a 160F stat lowers the steady state (say 50MPH cruise temperatures on a 68F day) down from 210F down to 175F refutes your above statement as the only thing that has changed is the thermostat, the cooling system is otherwise exactly the same.

I just had the opportunity to check a 2000 996 yesterday. Yes the dash gauge was inaccurate on the left side of 180. About 10 degrees worth. It seemed to get accurate about 190 and above. But the curious thing that I noticed is that the pulse width for the injectors didn't stabilize untill it reached 190. At 150 pulse width was 3.2 ms. At 190 it dropped to 2.9ms and remained at this value while temp was increasing. Does this not imply that it is tapering off the cold start network untill the thermostat opens. This would result in a perceived power increase (richer mixture) if the fuel trims didn't kick in. So the bottom line question is if you put in a lower stat would the DME think that the engine is still cold and not fully warmed up for the fuel control?

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The DME has the flexibility to deal with the car running slightly cooler without issue, plus the injector pulse at those temps is varying in response to the mixture delta across the three way cats as their temperature varies more than the coolant temp; plus we have had a number of customers that commented their fuel mileage increased very slightly after we installed a 160F stat, just as we have seen on the dyno. While the difference's in mileage and power are not very great, they seem for the most part to be reproducible, which could imply a very small improvement in the engine's efficiency with lower coolant temps.

I give up. Tomorrow I'll put a 30F thermostat in and my car will crap ice cubes. Over and out.