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Originally Posted by blue2000s
I appreciate the explanation. It's interesting info.
- Are there UOA results for both the standard and low temp t-stat for comparison?
Yes, we have installed several of these stats, including one in my own car, and run UOA's before and after. The actual test results are the property of the car owner's (they paid for them) so I can only provide summary info without their permission. We did not any see evidence of acid formation related issues, and we also did not see increased fuel dilution (another "old wife's tale" about lower the stat temp). In general, the oil looked like it had seen a lot less mileage that it really had, particularly in the cars that get the Hell beat out of them on a regular basis....
- What your explaining on the t-stat operation is that the engine won't run hotter than the fully opening temperature during cruising, which is essentially steady state at 72-74F. Keeping everything else equal, the water temp should go up linearly with air temp, so at 84F, the water will be 10F hotter, right? What temperature do the fans come on? Does the car run at a temperature independent of the t-stat at non-steady state like at an autocross or mountain road driving?
At any ambient temperature, the "steady state cruise" temp is a function of the ambient temp, air flow, radiator condition, air flow obstruction, etc. etc......as well as the full flow open temp of the stat. As you are an engineer, none of this should be news to you. On a hotter day, in bumper to bumper traffic, or under hard use, a car with the LN stat will still get warm and will eventually cause the fans to kick on (the function of which is controlled by the DME). But, when the increased airflow (either from the fans or movement of the car), the temps drop back down; the major difference is to where they go. In fact, one customer comment is that they notice that their fans do not seem to cycle as much as they did before the change. On my personal car, I saw the coolant temps rise yesterday (while stuck in traffic) to over 215F when the fans kicked in. As soon as I clear the traffic and was back to 65 MPH, the temps dropped back down into the high 170's low 180's range (ambient temps were in the 85F range). Note that I monitor the oil and water temps via a display from an aftermarket data logging system connected to the OBD II port rather than the dash displays, which are notoriously inaccurate and non linear on just about all Porsche models. To address your questions, yes higher ambient temps will result in higher coolant and oil temps, not necessarily in a linear fashion, but they will both be lower than when the OEM stat was used in the same vehicle under the same or similar conditions. When a car equipped with the low temp stat enters an adverse environment (traffic, track usage, etc.), it will start from a lower coolant temp and tend to take longer for the fans to come on, and will cool back down to the lower operating temp once the load condition returns to normal.
I definitely am not in this for a p*ssing contest, just to understand what's going on. I was an SAE member as well when I had my papers published there in in-cylinder flow simulation. I'm haven't been working in the auto industry for about 10 years so the membership expired a long time ago.
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