Water Pump and Thermostat

[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.

[JFP in PA]

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.

For someone that says "No argument", you definitely come across as someone spoiling for one.

That said, I would fully expect that a 160F stat is not going to do much for a car being flogged on a track. First of all, racing is never "steady state"; on the track, everything is changing all the time (air temp, RPM range the engine is seeing, the number of cars holding you up at any given moment, load on the engine etc.), which only adds to the confusion when trying to reproduce results; and the thermal load conditions that car is seeing is totally different than that of a what street car sees. And as my comments are directed at street use, which is where the low temp stat was designed for, they do not apply to a car used in track applications.

On several customer's 986 (we done this with both base and S cars, Tips and manuals), fully instrumented (read not using the factory displays) when equipped with the OEM stat and running at a steady prolonged speed (target speed of 40-50MPH) with an ambient temperature in the 68-72F range, we have tracked coolant and oil temps over extended driving periods. Nominal coolant temps tended to be in the 210-215F range under these conditions, with the oil running 20-30 degrees or so warmer. With no other modifications, the same cars produced steady state coolant temps of 175-180F by switching to the 160F stat, with a concomitant drop in the oil temps as well.

Will the street driven car heat up and turn the fans on if it gets stuck in traffic? Yes it will, but it will take it longer to do so, and will cool back down to the lower observed steady state temperatures once air flow over the radiators comes back and the car returns to cruising speeds.

So does using a 160F thermostat result in lower coolant (and oil) temps on a 986 driven on the street? Most definitely. We have also tracked UOA's on some street cars, before and after they were switched to the 160 stat, and observed slower oil degradation over time, which is probably attributable to the oil seeing consistently lower temperatures as well.

[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 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.

[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.

[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.