bwebb77

As I posted before I recently did a complete flush of the radiator and block. Installed both temp sensors and a new 83 C thermostat. I burped well. Car has been running a little warmer than normal. It was running a little above last line, where normally it is just a little under. Today I changed to a 75 C thermo and have been driving for four hours in traffic with a lot of stop and go. The AC was on all the time and temp is about 75 deg. today. The gauge never went above mid. I have had the shark since '89 and never has it been so low. I have always had problems with it getting very close to going red on me. I have to agree with Heinrich, I'll always use a 75 C now.

Fogey1

Did you happen to measure the _actual_ engine coolant temp with either thermostat? I.e., do you know what your guage means, where it's calibrated?

I once threw a bunch of anxiety, time, money and two thermostats and pressure caps at a car that had a bad sender to the guage. When I finally Dx'ed it and replaced the sender the "overheating" problem disappeared. I used a lab thermometer in the overflow stream to the coolant botle, but that was then, before remote IR readers.

Randy V

Watch your fuel mileage - let us know if it gets worse with the lower temp thermostat. Also, any decrease in performance.

A hotter engine typically is more efficient.

jpitman2

FWIW, I have been running a 75C thermo for a few years now, originally fitted because I was in 40C+ (104F) ambients a lot. Now I am back in more temperate climes (20-35C), it produces stable readings around mid gauge, acceptable consumption figures on the open road, and what feels like normal power - not that I am out there checking the red line regularly, but the LSD gets a work out now and then.
jp 83 Euro S AT 49k

Normy

I get about 13 mpg in the city these days, and I have the 75 C t-stat. The car used about the same in the city with the 83 C part, but whereas before I managed 22 mpg on the highway, now I'm lucky to get 21.

This part made a difference in my engine, dropping the needle from middle of the gauge to around the lower white hash mark. Of course, I've changed my coolant about yearly the past few years, and I have a clean, fairly new radiator.

N!

bwebb77

Randy no performance drop that was noticed. I'll post fuel mileage after a few tanks. My point was that my car always run hot, or what I thought was hot. If Porsche wanted higher temps then the guage would have been calibrated for it. Just got back from some more running around, little cooler now outside and the gauage is a little below mid. All things being equal I'll take the running cooler on the guage over the running very hot any day.

Imo000

In the summer or warmer climates a lower rated thermostat is a good idea. It will also leave the engine with a larger safety margin in case of over heating. A cooler engine will produce a more hp.

A hotter engine is NOT more efficient. The engine has to be just warm enough to operate properly. There is not that much of a difference between a 75C and an 83C thermostat. They are both adequate to make the engine operate above the required minimum.

General rule is to use the 83C in cooler climates. It will let the engine warm up a bit faster, but will also keep it warmer. On the other hand, a 75C is for warm climates where quick warm up periods are not required.

dr bob

This is a dead horse that gets beaten to death time and again...

Having a cooler thermostat makes the gauge read lower, which may give someone a false sense that the cooling system is working 'better'. It's not.

One might be lead to believe that the car will have more cooling system 'margin'. It doesn't.

Some thoughts:
The cooling system is limited most by the size of the radiator and the ability to circulate water through it. The thermostat determines the 'floor' temperature, the minimum that you want the car to run at. At some point, and it's about the same point within 10 degreesF with either thermostat, you'll be out of the range where the thermostat is limiting the amount of water flowing through the radiator. From that point on, it's all a test of how well your radiator is doing the job.

Overheating in our cars, at least the boiling point of the coolant, is around 240F. When the coolant boils, it does a slighly poorer job of transferring heat. Changing the thermostat temp doesn't change that.

How fast the car will go from the thermostat floor temperature to overheating varies very slightly between the two thermostat temps. Depending on what's actually limiting heat transfer and how severe it is, you might gain a minute with the lower temp thermostat. Maybe.

------

Many folks make changes on their cars and then presume that the one off-design thing they did is responsible for the massive "improvement" they see. To wit, folks who change the thermostat also typically change the backing o-ring, the coolant, and flush the old junk and rocks out of the block. They add Water Wetter, and the correct dose of coolant in distilled water. So what causes the car to actually have improved cooling capacity? Hint: It isn't the thermostat.

Want to have a cooler-running car all the time? Invest in cooling system repairs and maintenance. Flush the old junk out. Make sure the radiator is in new condition inside-- might mean that the tanks have to come off and the core needs to be mechanically cleaned or replaced. Make sure the engine is running right all the time. A little error in timing on the cams, a partially plugged injector, or other mechanical stuff will cause the engine to generate more heat per HP delivered, increasing the load on the cooling system. Fix that stuff!

Gas mileage will suffer with the cooler t-stat. Why? The engine brain thinks the car is not yet warmed up, and richens the mixture slightly to avoid leam misfire. A colder intake will make more ponies, but a colder block and heads will not.

heinrich

Hehe ... I got quoted