thermostat question

[sylvester]

Hello I have a question about a Porsche 911 SC oil thermostat.... my 79 SC never go down after normal driving. Will eventually overheat sitting still. but won't overheat driving at hwy speed. but stays in the white right above the red. I check right after external thermostat it's 150-160 degrees both lines. the trombone at wheel is 110-115. what could the problem be thank you for your help.

[Steve@Rennsport]

I would remove the thermostat housing, remove the element and test in boiling water to make sure its opening ALL the way above 185 deg F.

[sylvester]

OK... that's a big ten four sir. I'll try that out and return back here thank you.

[GeorgeM]

If it overheats standing still, might the engine mounted thermostat be bad as well?

I had the opposite issue with my 3.2. It would never get fully up to temp. After replacing the temp sender, I tested the engine mounted thermostat and it appeared to work, but I swapped the guts out anyway and, voila, problem solved. Now it gets up to about 180 in reasonable time and stays there.

[ossiblue]

Originally Posted by sylvester

Hello I have a question about a Porsche 911 SC oil thermostat.... my 79 SC never go down after normal driving. Will eventually overheat sitting still. but won't overheat driving at hwy speed. but stays in the white right above the red. I check right after external thermostat it's 150-160 degrees both lines. the trombone at wheel is 110-115. what could the problem be thank you for your help.

When you post the temp "right after the external thermostat," do you mean on the engine side of the thermostat? If so, it appears as if the external thermostat may not be opening at all.

When closed, the external thermostat allows oil to flow up to the front cooler and back to the thermostat housing, but not into the tank. Oil from the engine circulates into the tank through the bypass in the thermostat thus the oil is only being cooled by the engine oil cooler. This would account for your 110 temp at the front cooler--static oil being cooled by the air flow around the lines and the cooler--and the hot temps on the engine side of the external cooler--circulating oil being only cooled by the on-engine cooler. The fact that the oil overheats when at idle also could indicate the oil is only being cooled by the on-engine cooler which now has little cool air passing through it.

Do as suggested and remove/test the external thermostat as that sounds like the most likely culprit.

[gomezoneill]

This may help you
How External Oil Thermostat Works - Illustration