Engine Thermostat, Low Temperature (begins opening at 160 deg F)

[JFP in PA]

OK, first let’s clear up a couple of misconceptions: First, a lower temperature thermostat regulates the lowest temperature the engine will run at, not the highest. That said, cars running the 160F stat tend to run substantially cooler in a “steady state” condition (open road, constant speed recorded temps in the mid 170’s are common). Stuck in traffic, a car with the 160F stat will heat up just like one with the OEM stat, but it will take longer (starting from a lower temp), and will eventually cool back down to the lower steady state temp once the car is moving at speed again. Second, the OEM stat opens at 186F, but the car runs much hotter than that; usually in the 210+ range (the dash gauge is woefully inaccurate). It is not unusual for a car with an OEM stat to have coolant temperatures well north of 200F at the same “steady state” conditions. Third, these cooling system’s have documented “hot spots” in them where the coolant sees even higher temperature’s due to flow restrictions in the system, etc.; running the lower temp stat (and the inherent lower coolant temp) help reduce the temperatures at these hot spots somewhat. Fourth, the cars do not take any longer to warm up, temp rise from startup is a function of the initial ambient air temp and the volume of coolant, neither of which is altered by changing the thermostat. In fact, many owners comment that the car appears to warm up more quickly with the low temp stat, which is an illusion created by the coolant beginning to circulate sooner (the gauge moves sooner, heat comes out sooner, etc.). In actuality, once the stat opens, the 160F stat slows the process down as it begins to transfer heat out at the radiators, but that creates no issues, contrary to most “urban legends”. A lot of people seem to believe that running the lower temp stat is going to foul the oil with water and unburned fuel; but that simply does not happen as repeated used oil analysis have proven; the oil still gets plenty hot enough to flash off any volatile’s, as it is under a constant vacuum condition any time the engine is running. Perhaps more interesting, UOA’s have shown that just going to the 160F stat lengthens the oils life, most likely due to the fact it is typically running 20-30 degrees cooler most of the time.

Outside of lowering the engine and oil temperatures, the other major advantage to running the car at lower temperatures is a slight but measurable improvement in volumetric efficiency of the engine and reduced pre-detonation characteristics. On a normally aspirated engine, this would show up as slight but measurable increases on a dyno, but is more commonly noted in real world driving as a slight improvement in fuel mileage.

Another point worth pondering is the fact that Porsche uses the same low temperature stats in some of their production cars: GT2, GT3, and the Turbo…….