Water Pump and Thermostat

[mikefocke]

So both are right under different scenarios?

Reading you both...

The low-temp isn't going to let more coolant through to the radiator (just sooner) but in the low speed running low thermal-loaded state the temps will be lower thus when the engine needs more cooling the radiator coolant starts out from a lower base.

Raise the temps toward or to the thermal max of the radiator (as in racing or A/C on on a hot day) and the low-temp thermostat will have no effect as the same coolant flow will get to the radiator and the radiator will cool to its max (if the leaves have been cleaned out).

It will take a while for the coolant to return to lower temps (because that only happens when the radiator can remove more heat than the engine is producing) even at low thermal-load road speeds but the low-temp thermostat will allow eventual return to a lower state.

On a road car, the oil will last longer because it spends more time at a lower temp.

So I'm left with the questions:

What is the real coolant temp difference between running at a constant 40-50 MPH and 70?

Once you raise the temps to the max the radiator can handle, how long at a moderate speed does it take for the temps to drop to the point where the low-temp thermostat makes a difference?

How much does the ambient temp influence the max cooling capacity of the radiator? IOW, how hot does it have to be out on a road car (because most of ours are) before the low-temp makes no difference after warm-up?

[Pdwight]

and quite a bit of good information here to be had...many thaks guys.

So what is really happening is the Bell Curve of the operating temperature will just be different with the lower T Stat due to it opening sooner....been a long time since statistics.

[j.fro]

This is turning out to be a great thread!
So...if we weren't interested in the heater ever working, why not get rid of the T- stat all together? What do race cars need them for?
I think I know the answer, but I want to hear from the experts.

[JFP in PA]

Originally Posted by mikefocke

So both are right under different scenarios?

Reading you both...

The low-temp isn't going to let more coolant through to the radiator (just sooner) but in the low speed running low thermal-loaded state the temps will be lower thus when the engine needs more cooling the radiator coolant starts out from a lower base.

Raise the temps toward or to the thermal max of the radiator (as in racing or A/C on on a hot day) and the low-temp thermostat will have no effect as the same coolant flow will get to the radiator and the radiator will cool to its max (if the leaves have been cleaned out).

It will take a while for the coolant to return to lower temps (because that only happens when the radiator can remove more heat than the engine is producing) even at low thermal-load road speeds but the low-temp thermostat will allow eventual return to a lower state.

On a road car, the oil will last longer because it spends more time at a lower temp.

So I'm left with the questions:

What is the real coolant temp difference between running at a constant 40-50 MPH and 70?

Once you raise the temps to the max the radiator can handle, how long at a moderate speed does it take for the temps to drop to the point where the low-temp thermostat makes a difference?

How much does the ambient temp influence the max cooling capacity of the radiator? IOW, how hot does it have to be out on a road car (because most of ours are) before the low-temp makes no difference after warm-up?

Mike, the difference between 40-50 and 70MPH is not substantial in terms of the "steady state temperature of the coolant, but the rate of change (how quickly the car will cool from the heavy traffic temps) when coming out of traffic onto an open road is higher for the car going 70 due to increased air flow over the radiators.

At an ambient temp range of 68-72F, it will take a few miles for the engine to shed excess heat with either stat, but what does happen is that as you approach the nominal "steady state" temp of either stat, the thermostat begins to throttle the coolant flow a bit, so the rate of change gradually slows and begins to cycle up and down slightly until is settles at the nominal steady state temp. Because the available heat transfer rate is basically constant (limited by the radiators and air flow), the OEM stat will reach its steady state temp sooner than the 160F stat will as it does not have to shed as much heat.

Ambient temps do have a significant impact on cool off rates; a car running in 40F air will cool much quicker than one in 80F air. But in either case, again at steady state, the car with the 160F stat will be running much cooler than the OEM stat; the only thing that really changes is the delta or rate of temperature change attributable to the difference in air temps.

[JFP in PA]

Originally Posted by j.fro

This is turning out to be a great thread!
So...if we weren't interested in the heater ever working, why not get rid of the T- stat all together? What do race cars need them for?
I think I know the answer, but I want to hear from the experts.

You can actually flow too much coolant at higher RPM's, and when moving too quickly past the radiators, will not have time to shed enough heat. A lot of racers replace the thermostat with a thin metal disc with holes drilled in it to control the flow rate without any chance of the unit failing as a thermostat can do at the most inopportune moment. Trick with using the metal plate is to find out how many of what sized holes are "just right" for your car with a given track and air temp. Going this route will also drastically slow the engine warm up time, particularly as the air temps drop.

[Reebuck1]

Thanks JFP.....very informative to DYI'er like us....THANKS !!!

[epapp]

I agree with all of this, I think we were all saying the same, mostly correct things, just talking about different sides of the argument.

Now the thing I am curious about is: running oil at a cooler temp (to a point) is a good thing, no contest. But running the coolant COOLER than what the ECU is expecting as a 'warmed up' engine could also be bad. Fuel trims are different based on engine temperature, and the tstat being a 180 degree tstat is that way so that the M96 can run at the CORRECT heat based on its sensors and fuel map, metal composition, expansion factors, tolerances, etc...right?? Seems like running at a lower temp (to a point as well) could also be bad, in the best case, potentially just worse fuel economy?

[JFP in PA]

Originally Posted by epapp

I agree with all of this, I think we were all saying the same, mostly correct things, just talking about different sides of the argument.

Now the thing I am curious about is: running oil at a cooler temp (to a point) is a good thing, no contest. But running the coolant COOLER than what the ECU is expecting as a 'warmed up' engine could also be bad. Fuel trims are different based on engine temperature, and the tstat being a 180 degree tstat is that way so that the M96 can run at the CORRECT heat based on its sensors and fuel map, metal composition, expansion factors, tolerances, etc...right?? Seems like running at a lower temp (to a point as well) could also be bad, in the best case, potentially just worse fuel economy?

Has not proven to be the case with a 160F stat. The DME has the leeway to adjust the fuel trims from cold start (often very cold) to running in Death Valley conditions., as well as adjusting for pretty large changes in altitude. If the DME ever "ran out of rope", the car would start coding because the computer had reached its limits; I have never seen or even heard of that occurring with a low temperature thermostat. You need to also not that the "high output" Porsches (Turbos, GT cars) run 160F stats from the factory.

I've also not hear of anyone suffering decreased MPG as the result of using one of these units; and in fact have had customers comment that they feel they are seeing a small but reproducible increase in fuel mileage. I don't really know how real that is, but after several different customers commented on it, you have to take note of it.

[epapp]

I didn't mean that the DME would run out of rope, I realize it has the ability to adjust fuel trims to many temperatures and altitudes. What I meant was that it would stay in some 'almost-warmed-up-fuel-trim state' by allowing the engine to cool to around 160 when on the freeway in low load conditions etc....because the DME expects 180 (186) minimum to be the steady 'warmed up' state on our cars.

Unless of course the DME doesn't think 186 is warmed up, but rather something lower. It depends on the fuel map vs. coolant temp. In a graph of those two, there is some temperature when the DME stops considering the car 'warming up' and changes its fuel trims accordingly. It very well could be below 160, in which case running the 160 thermostat would help in some circumstances to lower the coolant temp.

Which makes me think...why fit a 180 tstat at all? If running lower than 180 is better in some cases and doesn't affect the engine warmup fuel trims, why even put a tstat in the car from the factory that makes it run hotter? Also, why let the car heat up to 212 before turning on the fans?

[seningen]

Originally Posted by epapp

I didn't mean that the DME would run out of rope, I realize it has the ability to adjust fuel trims to many temperatures and altitudes. What I meant was that it would stay in some 'almost-warmed-up-fuel-trim state' by allowing the engine to cool to around 160 when on the freeway in low load conditions etc....because the DME expects 180 (186) minimum to be the steady 'warmed up' state on our cars.

Unless of course the DME doesn't think 186 is warmed up, but rather something lower. It depends on the fuel map vs. coolant temp. In a graph of those two, there is some temperature when the DME stops considering the car 'warming up' and changes its fuel trims accordingly. It very well could be below 160, in which case running the 160 thermostat would help in some circumstances to lower the coolant temp.

Which makes me think...why fit a 180 tstat at all? If running lower than 180 is better in some cases and doesn't affect the engine warmup cycle, why even put a tstat in the car from the factory that makes it run hotter? Also, why let the car heat up to 212 before turning on the fans?

I'm pretty sure it has to do with emission testing.

I could be wrong -- but thats my best guess.

Mike

[epapp]

Thats a good point, getting the engine up to temp faster would reduce emissions

[JFP in PA]

Mike is correct, it is done purposely for emissions. The quicker the car gets hot, and heats up the cats, the faster it falls into the emission "zone".

Interestingly, we ran a couple side by side scold start essions on the rollers with sniffers in the exhaust, and saw very little difference between a car with the OEM stat and the lower temp unit, other than it took a couple extra seconds to line out at the same final values.

[DennisAN]

In most cars a "low temp" thermostat is a bad idea. But in the water cooled Porsche engine, the thermostat is put in an oddball location. Most cars put the thermostat in the EXIT port where the hot coolant leaves the engine going off to the radiators. In the Porsche engine, the thermostat is put in the INTAKE port where the (cooled off) coolant returns from the radiators and enters the engine. Perhaps this is why the low temp thermostat is helpful.

I've never figured out why the Germans put the thermostat in that location. IIRC my VW Scirocco and Jetta did the same thing Porsche did. The Americans, British, and Japanese all put the thermostat in the output port, so that hot water goes off to the radiator.

[epapp]

Originally Posted by Brad Roberts

NO argument

Show me. Show me the test case, test scenario. I have 4-5 years of AIM and Motec data logs showing ZERO decrease in water temp. My logs are 25-30min logs and multiple 3-4 hr logs. With and without 3rd radiator, with and without BoxsterS water lines. With and without standard coolant (with/without water wetter)

I *know* you know better than to read the gauge for this. Show me


We are racing. I have steady state consistent lap times in all sorts of different weather. I'm suspecting what your seeing only pertains to certain circumstances.

Whats your results from using water wetter? I've always wanted to try that stuff, but that was around the same time I experimented with marvel mystery oil

[JFP in PA]

Originally Posted by epapp

Whats your results from using water wetter? I've always wanted to try that stuff, but that was around the same time I experimented with marvel mystery oil

Water wetter, or what ever brand name you choose, is just a surfactant mix to lower the surface tension of water. If you are using a water/coolant mix, it is unnecessary as the coolant already carries similar capabilities, and not all of the commercial products maybe compatible with Porsche coolants.

[DennisAN]

IIUC you aren't allowed to use antifreeze on most race courses - it would make the track slippery if spilled all over after a crash. So you can use water wetter with distilled water for coolant there. That wouldn't create a hazard.