Low Temp Thermostat Works as Advertised

There has been debate on this and other forums as to whether a lower temperature thermostat is effective in reducing engine temperature. I have data that proves it is effective, and I wanted to share that information with the forum. First, some important info: Factory Thermostat Begins opening ~185F Fully open ~205F Low-Temp Thermostat Begins opening ~165F Fully open ~185F Also, I have added the 3rd radiator to the center grill. I participated in a BMW CCA "Club Racing School" event at Mid-Ohio Sports Car Course with my 987.1 Cayman S this weekend. I used an OBD II sending device in tandem with Harry's Lap Timer to the read real-time coolant temp data from the ECU. Unfortunately the data could not be logged, but I can record the max reading and I kept a very close eye on the number while driving. The third day of the event was our 25minute "mock race". Ambient temp was 75F. My peak coolant temp measured 201F. This means that my low temp thermostat, in combination with the 3rd radiator, was able to maintain coolant temps BELOW the temp at which the factory tstat is even fully open. How is this possible?? The lower temp thermostat begins to open 20F sooner, and is fully open at least 20F sooner than the factory part. Meanwhile, the engine creates the same amount of heat lap after lap as it always did. But now, when the low-temp tstat begins to open, the engine is exposed to coolant that is 20F cooler than with the factory tstat. This cooler coolant is able to absorb more waste heat from the engine and carry it to the radiators where that waste heat is dissipated. Therefore, as long as you have enough heat dissipation capacity in your cooling system (ie: a 3rd radiator), then you will see a benefit from a low temp thermostat. For a $75 part, I think this is a good investment for anyone who regularly uses their car on the track. It's even more effective when used with a 3rd radiator.

Matt, Thanks for the info. However, one problem I see is that the low-temp thermostat and 3rd radiator were not tested separately to see which works and which doesn't. In other words, for all we know your result was from the 3rd radiator and the low-temp thermostat had nothing to do with it. I'm not saying that's what happened, but based on your testing it's impossible to tell... 3rd radiator has been proven multiple times to reduce the coolant and oil temp, so your test results don't necessarily tell us that low-temp thermostat works. Still, good job with data logging and sharing.

Actually, we can conclude the low temp tstat had an impact in addition to that of the 3rd radiator. The OEM tstat isn't fully open until 205-210F. My temps never reached that point. One could conclude that with the OEM tstat, the peak temp would always have to be at least 205-210F under track conditions. If my 3rd radiator cooled my water temps below that level, the factory tstat would begin to close and try to maintain that 205-210F temp. That was not happening while I was on track, because the low temp tstat doesn't begin to close again until 185F. The majority of the time I was out on the track, my temps were in the low 190's. The fact that I was in the 190's most of the weekend, with a peak of 201F during a 25 minute simulated racing session confirms the low temp tstat will run cooler if the rest of your cooling system is able to effectively dissipate heat. To your point...I'm not sure that the low temp tstat would perform any differently than the factory one without the 3rd radiator. The low temp tstat opens at lower temperatures, but the 3rd radiator is what helps dissipate the heat and maintain the initial advantage the low temp tstat provides.

I see what you're saying. Good points. :cheers:

I'll drink to that! :beer: So for under $500 ($75 for tstat and ~$350 for 3rd Radiator kit), 987.1 owners can keep their coolant temps below 200F under track conditions (ambient temp was 75F that session). This is HUGE, as it means my peak oil temps was likely in the neighborhood of 220F-230F...well within the range of what any quality 40wt or 50wt street oil can handle.

Also, Vetman, I was just going through old PM's...did I sell you a set of 18" N-spec Pilot Sport 2's last winter?? If so, how are they working for you??

Well.... my dealer said they were dry rotted... Not all that big of a deal as they worked fine on both the street and the track, and the car it belonged to has been sold awaiting pick up...

I have not figured out the fascination with lower temperature thermostats. Cooler is not better unless you are in a temperature range that is too high. Third radiator = more heat rejection capacity. A good thing if the cooling system would otherwise not keep up (which is the case with these cars when pushed hard in hot conditions; I "hear" Miller Motorsports in July is a problem ). A lower temperature thermostat has a couple of potential effects: Maintains coolant temp below design value = not beneficial. If the motor was better or more efficient at lower temperatures, the stock thermostat would be set for a lower temp. 201 deg versus 205 deg does not scream "improvement" to me. Buys some extra time if the coolant temp would otherwise get too high = potentially beneficial, but only for a short time. Eventually if the cooling flow cannot keep up with the heat, temp will reach the same steady state with both thermostats. Adding cooling sooner (lower temp thermostat) means the motor will take longer to reach steady state so might buy you a little time.

My Cayman is regularly exercised at the track. My main concern is engine durability, and the biggest way to help that is by managing engine heat. A stock cooling system on a 987.1 has shown measured coolant temps north of 240F, with oil temps approaching the 270F range under track/racing conditions. At that temperature, some oils can begin to shear. More than one experienced M96/97 engine rebuilder believes this to be the root cause of the #6 piston/rod failures we're seeing with these motors. The "design value" Porsche selected with their stock thermostat strongly considers emissions levels. A hotter engine, to a point, helps contribute to more complete combustion and lower emissions. That's great for a street driven car and an owner who is concerned about MPGs and CO2 emissions. At the track, I'm more concerned about managing engine heat and maximizing engine longevity...as I spew emissions and burn that 93 octane at a rate of 9.0MPG, or 4gal per session. My measured 201F is proof that a low temp tstat + 3rd radiator can maintain engine temps lower than a 3rd radiator with the factory tstat...because the factory tstat will always read higher than 205F. With a factory tstat, I would likely have been significantly hotter than 205F; closer to 215, 220, or higher. I didn't collect that data because that's not the experiment I was running. I was simply trying to measure whether I could maintain coolant temps below the point at which the factory tstat is fully open (205F). This would prove that the low temp tstat has a positive impact on managing engine waste heat. It is interesting to note that 996/7 GT3 & Turbo, and 987.2 all use a lower temp thermostat than 987.1 cars. One might conclude this is because the GT3 and Turbo cars are built with track performance in mind. The 987.2 cars are DFI and so combustion efficiency/emissions can be managed more precisely without having to force the motor to run at higher temps like the non-DFI motors. I agree that if the rest of the cooling system can't keep up with the heat, the low temp tstat won't help. It needs the 3rd radiator to be most effective. BUT, a low temp tstat PLUS a 3rd radiator will run cooler than just a 3rd radiator, as I have shown. It's not just adding cooler coolant to the system earlier; that advantage is maintained by allowing the system to be open by 185F. Because the radiator system can effectively dissipate the heat, the advantage is maintained. My measurements were taken during a 25minute sprint race on a 75deg day; I think it's safe to say that the low temp tstat did more than just buy me a little time. At the end of the day, I've collected the data that I needed to prove this point for me. I wanted to share that information with this group because I know there are others out there who regularly track their cars and will happily spend $75 on a part that can maintain lower coolant temps when used with a 3rd radiator.

Where did you get this lower temp thermostat? Do you have the part #?

LN Engineering sells them, and I believe they sponsor this forum if you'd like to support them. I bought mine from Pelican parts as part of a larger order involving parts that LN does not carry.

There is no benefit to the low temp thermostat for heat dissipation. Sure it will open earlier but once it opens there is no difference. If you didn't add the 3rd radiator it would be a complete waste of money. Actually is is still a waste of money even with the 3rd rad. The engine is designed to work in a certain temp range and the stock thermostat maintains that temp. Lets not confuse temperature & heat . As the coolant temp goes up the delta T between the radiator and the ambient air goes up and more heat (BTU) is removed from the coolant and engine not less.

Great job on the review. I installed the LN low temp tstat along with water wetter last year and it worked very well ... the 3rd rad will be in installed later this month before the 1st track day ... can't go wrong with this mod if you are planning to attend several track days.