[Walt Fricke]

David:

Oil temps of 210*F are just fine, especially so with modern synthetic oils.

The thermostats seem to open at 190F, more or less, from my observation. There is a school of thought that you don't want to run all the time below 210, because then you won't boil off any water which has gotten into the oil - and some does despite the car being air and oil cooled and not water cooled.

I wasn't aware that Porsche changed the opening temperatures of its thermostats, so I looked into my Factory Shop Manual. Starting with the 1969S there are two thermostats - one in the engine, one external for the front cooler. Both involve wax heating up and pushing a sort of piston out of a capsule. While the two thermostat housings are geometrically different, the capsules are the same in both. The parts manual gives a part number for the capsule in the external thermostat, but not the engine mounted one, which is just shown as a complete unit.

The early engine mounted thermostat units had a screw adjustment extending out the top of the unit. You can see this in the pictures in the Volume I shop manual. I suppose if that adjusted the capsule position relative to the valve it controls that might affect the opening temperature? The factory manual makes no mention I could find about adjusting anything with this. It does say the original thermostat is set to open at 80*C (176*F).

Starting with the 1969S model (first to have a front supplementary oil cooler), the front cooler thermostat opens at 87*C (189*F). The engine thermostat opens at 83*C (183*F).

I've tested these thermostats and capsules, but just using a refrigerator for cold and boiling water for hot. Those were go/no go tests to see if a capsule had quit working (which they do) or not.

Not a word is said about that mysterious adjusting or something screw in the early engine thermostats. Unlike the external thermostat, the engine one is not set up for straight forward disassembly, though I have seen reference to being able to do that.