Why I installed a low temp thermostat.
 

I know that the controversy over whether to use a low temperature thermostat gets almost as heated (pun intended) as which oil to use, but here goes.

When I first read about the low temperature thermostat, I wasn't convinced. I figured the thermostat really did not make much of a difference, since the coolant temperature is really limited by the capacity of the radiators and the temperature at which the fans go on. But after reading way too many posts on the subject, and most recently the Hartech article (see below), I went with the Wahler 160 thermostat.

What really convinced me was the inherent flaw in the 9X6, 9X7 cooling system, namely, that the thermostat and the coolant temperature sensor both receive coolant only after the coolant has gone through the radiators, coolant that is is at its coolest. The hot coolant exits the motor, goes through some long plumbing to the two radiators up front and back through some long plumbing before it reaches the thermostat and temp sensor, nice and cool. But the coolant around the cylinders and heads will be much hotter than what the temp guage reads, because the temp guage is reading coolant that already went throught radiators.

In addition, the stock thermostat begins to open at 86 C and is fully opened around 99 C, so the thermostat is partially opening and closing when the coolant is almost at the boiling pioint. And remember, that is coolant that is already gone through the radiators and cooled down. The coolant in the motor around the cylinders and heads will be hotter than the coolant going into thermostat.

So what happens? You are on the open road with sparse traffic, going a leisurely 75 miles an hour in fifth gear. Because of the very good airflow at that speed, the radiators are working at their optimum, and the coolant is cold enough so that the thermostat is closed, or is partially closed. So you decide to downshift to third and get on it, to pass a car, or just for the fun of it. The moment you open the throttle and start approaching the redline, the cylinders almost instantaneously get significantly hotter. But the thermostat is partially closed, impeding the coolant flow. More more important, the coolant that is trapped around the cylinders and the heads was already significantly hotter than what the temperature gauge reads, and getting hotter by the second. And since the hot coolant in the engine has to go through all of the cooling system plumbing and the radiators before it gets to the thermostat, there's going to be a significant lag time before the thermostat opens fully to allow the full flow of cooler coolant to get to the now very hot (and getting hotter) cylinders and heads. What you now have is a condition that is perfect for a localized hotspot in the cylinder or heads.

With the low temperature thermostat, the coolant flow in the above situation will always be at its maximum, since the thermostat will be wide open at cruising speeds. So that when you cane the motor, you are getting the maximum flow of cool coolant over the rapidly heating cylinders and heads. The low temp thermostat ensures better cooling during a high load, high temperature acceleration, which after all, is what our cars are all about, right?

So that's my story and I'm sticking to it.

http://www.hartech.org/docs/buyers%20guide%20web%20format%20Jan%202012%20part% 205.pdf

low temp
 

I agree with what you're saying. And to add to it, I live at 4600 feet, the air here is lacking density. Also very dry here. My thinking was that I could use all the help I could get as far as cooling, and the low temp seems to be working for me. Of course its winter, at least on the calendar, and summer might be different. I already toasted one engine due to heat problems.

My wife's 2.5 runs hotter than my 3.6. It makes me crazy when I drive her car in the summer. I spend the whole time trying to will the gauge down to 180.

What you say makes sense and I have no reason to doubt that cooler is better. That said, the eminent engineers at Porsche seem to know what they've been doing for over 50 years. I have seen no insinuation or suggestion that heat has in any way damaged the Porsche engines. Do you have any idea what issues may have been caused by the factory system?

That Porsche will admit to? None. But according to Planet 9 there have been some Caymans with cylinder 6 scoring, leading to loss of power and excessive oil burning. Hartech believes the problem is a redesigned (different from ours) head gasket that provides less coolant to cylinder 6 (the most vulnerable since it is the farthest from the coolant inlet) compounded by the already high coolant temperatures because of the 86 deg. thermostat.

*subscribed*

I'd like to see where this discussion goes as I've just installed a low-temp stat as well.

To me it is in the same category as the underdrive pulley. Possible benefit but not so much that would compel me to do the modification unless something else needed attending to which would provide access for the change.

Ok, I'll bite.

I'm not sure that it works as described. When driving down the interstate at 75mph and then jumping on the throttle, the coolent continues to flow at the full rate. The closed thermostat does not slow or hinder coolent flow, it only redirects it (to the first order of operation).

Thus, the theoretical instantaneous spike in coolent temp that happens when the throttle opens isn't real because relatively cool coolent is circulating continuously at full flow at all times and is maintained at a constant temp as the thermostat incrementally opens to divert the some of the now warmer coolent to the radiators to maintain it.

If (and that is a big IF) there is a local hot spot within the engine, then that is a result of poor flow design and is unlikely to be fully mitigated by using a lower temp thermostat (will help under some conditions but not help under other conditions).

The fact that the temp sensor is on the "cold" side of the cooling system is a red herring (meaning irrelevant) because the thermostat operates entirely independent of the gauge reading, i.e., the stock thermostat starts to open at 180F regardless of what the coolent temp gauge reads. Moving the gauge to anywhere else in the coolent system will not change the cooling system performance.

With all of that being said, I definitely agree that heat is the enemy of an engine and better engine heat management is always a good thing! :cheers:

Shouldn't we also be talking about the benefits of adding the center radiator to the non-S cars that don't have it?

Usually I would agree with that statement.
But please remember ours was the first water cooled flat 6 they ever built ....

But far from the first water cooled Porsche.

15 years ago and, to my knowledge, not only have the original late 90's done fine - but they haven't felt a need to change it. Again, as I've stated above, I agree that a cooler running engine is probably better but I don't see any proof that the temperatures are detrimental to the engine. Additionally, as stated above, the thermostat operates on temperature not on the digital readout.

The thermostat failed to open on my 190SL one summer day and I didn't see the
temp. guage climbing - in a few minutes the rad cap blew and so did the head gasket. A costly repair including a head rebuild later I installed a failsafe thermostat - 72c . These thermostats fail open. I used that thermostat for six years and never had another problem.

I'm certainly not saying that the temp sensor has anything to do with regulating the thermostat opening. I was mentioning it to illustrate that the temp sensor doesn't show the temp of the coolant around the cylinders and heads, which is critical, it only shows the temperature of the coolant at its coolest temp, after the coolant returns from the radiators. So you look at the temp guage and say to yourself that the coolant is not hot, but what you see is the temp of the coolest coolant in the engine, and not the temp of the hot coolant around the cylinders and heads.
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If I understand you correctly, are you saying when the thermostat is closed, that cool coolant is still getting to the cylinders and heads? How can that be since there will be a lag time before the hot coolant makes its way through the radiators to open the thermostat and allow cool coolant into motor?

All thermostats, Chevy, Ford, Ferrari, Porsche.... can fail to open. It just doesn't happen very often.

For what its worth, other modern P cars, the GT2 and GT3s, IIRC, have 160 deg thermostats.

Yep, at 94K miles my original water pump began to weep a bit and since it is a known weak link, it had to go. While we were in there a new motorsport 160F T-stat and a few idler pulleys were replaced. 90% of this job is getting the car in the air, accessing the work area and draining and refilling the coolant. I do tend to use ALL of the car so a fresh 160F T-Stat at 94k was a no-brainer.

Would I have gone to the trouble of changing a working T-Stat if my car was only 4 years old, had 20K miles, and the water pump and coolant looked great? Nope.

Replacing the t-stat was a piece of cake. Just clamp off the hose to the t-stat, take the hose off the housing, about 2 quarts of coolant comes out. Remove 4 bolts from the housing and its off. Reverse to install.

So did you change out that POS water pump while you were in there?

Where can we get the Wahler 160 thermostat that will fit in the Boxster ? How much did you pay for it ?

Did that last summer.