[cnavarro]

I personally tested the low temp thermostat in the dead of winter, and I can tell you, there were few days with wind chill at -34 F and the car warmed up very fast AND there was plenty of heat. There is a separate set of lines that go to the heater core and are being fed water regardless of thermostat state, so you will receive heat at the same time regardless of what thermostat you have.

At speed, even on a hot day, a 15 deg F drop in operating temp is normal on a car without a center radiator. That figure can be higher, up to about 20+ deg F with the center radiator.

But, to keep the coolant temperature down airflow is needed across the radiators. So if you're in traffic, coolant temp will creep up to the temperature where and when the radiator fans kick in, so at or around 205-210F. With the A/C running, they kick in harder, faster. Experienced this myself just yesterday at the Chicago PCA Autox.

I run instrumentation on my wife's Boxster and i've seen at times upwards of a 15-20 deg F difference in coolant temperature between the gauge and what the OBDII metrics read. I've also noticed the hotter the engine gets, the larger the variation. Just like the OBDII shows the speedometer is 6 mph off at 60 mph!

If I were to take a stab at why these cars come with such high thermostats is that they are trying to get the oil to run hotter, at or above 210F, to get the moisture out of the oil. By doing so, there is less acid formation and the oil retains its TBN reserve longer, allowing for longer drain intervals (as evidenced by Porsche's desire for initial 24000 mi target drain intervals). My own observations have shown that oil temperature is 10-15F over that of the coolant temperature.

Although I don't think this is the reason behind the high thermostat opening temp, additionally, having the oil hotter also reduces the viscosity, which technically would slightly improve fuel economy. But the flip side to that is by running cooler, you are increasing the volumetric efficiency of the engine, which makes power more efficiently.

Coolant temperature does not go up (or down) linearly with ambient air temperature, unlike cylinder head temperatures on an aircooled Porsche. The best explanation of what increased ambient air temps do on a watercooled Porsche is increase the amount of time it takes to lower the coolant temperature back to its initial point. The colder the day, the faster (and closer) the coolant temp can get to the point where it stabilizes. On a really cold day, that's 172F or when it's bloody hot, around 178F, for the low temp tstat, on one of Jake's 2.5->2.9 engines running 12.8:1 CR on pump 93.

Did I answer everyone's questions?