ZCAT3

I have read all the threads my archive search pulled up and still have not been able to answer a basic question: when does the termostat mounted in the rear passenger fender open to allow flow to the front cooler? My 87 Carrera seems to be running hot (at least compared to my 930) and yet the oil lines to the front cooler are not even getting warm. Yesterday I saw 9 o'clock on the temperature gauge (about 105 Celsius, 220 F) driving on the freeway in 90 plus degree heat - this seems high to me. When I returned to my home along the coast (maybe 20 degrees cooler) the temp gauge had dropped down to the first white line. I got out and felt the oil lines to the front cooler and the front cooler itself and they were not even warm. I let the car idle until the 9 o'clock position again, and still no oil to the front cooler. Is this normal? I have spoken to 2 mechanics. The obvious answer is the thermostat has failed and needs to be replaced. Both mechanics say this is very rare, however. Should I just let the car idle to the red mark and see if the damn t-stat finally opens? Maybe I will hear that mystical fan noise as well.

Bill Verburg

Nominaly, 85 degrees Celsius

ZCAT3

Thanks Bill - so is it fair to say the t-stat is not working? I can buy the internal thermostat for about $40 but I cannot seem to get the damn housing open. The whole assembly is $340 list - which I can get for about $230. I sure would rather spend that money on a Turbo S steering wheel or strut tower brace.

Bill Verburg

If the oil lines to the front aren't too hot to hold your finger on after a good long drive, then the t-stat isn't working. They do go bad. I don't know why, the control mechanism is just melting wax. The standard fan opens at a relatively high temp(maybe ~240F). Never having had one I don't know the specifics, but there is a way to have the fan come on at a lower temp, it's in the archives either here or at Pelican. But that is a separate issue from the oil line t-stat. By the way the t-stat for the engine mounted cooler also nominaly opens at ~85C.

ZCAT3

Well I was able to get the T-stat to open, but the temp appears to be around 220 F. The fan then comes on around 240F. I tried the same test with my 930 and the T-stat opened a little lower - maybe 210 F. I could not get the 930 warm enough to trigger the fan as the temp maxed out around 240 and stayed there.

quicksilver

I don't really see any thing to worry about from an engineering point of view if you are hitting 220º. If you don't exceed the boiling point there is a problem with condensation in the oil. Water in the oil can cause help oil to form acids when the it breaks down. It isn't a real problem in most cases but in a Porsche we are expecting a long service life out of the motors and most people seem to let there 911s sit between outings. Besides, 911s have a longer than average period between oil changes.

With modern oils 250º+ is bad because you are going to be seeing spot temperatures of 300º around the exhaust valves and from friction shear at the rod bearings. Anything below that should be fine. I would worry more about an engine that is babied to the point that the oil isn't heated.

ZCAT3

From what I have been told the T-stat should open flow to the front cooler at around 185. As I know that the t-stat is opening, should I just replace the thermo switch inside the mechanism? Is yes, does anyone have some tips for getting the thermo switch cover open (this is the piece that looks like a giant flat screw head on the thermo-stat housing).