Thermostat? '79 911sc

[Windsor4273]

I am new to air cooled cars so the engine cooling system has me confused. I realize the engine is cooled by air/oil, but how does it regulate its temperature? Is there a thermostat for the oil?

My temp gauge never seems to move unless it is really hot outside and even then it only gets barely above the "cool" mark. This never concerned me much, but it looks like the Porsche is going to become my winter car and I doubt it running around at lower than optimal operating temp is a good thing.

I am also not getting any warm air through the vents even after driving the car for a half hour or more. It blows plenty of warm/hot air through them in the summer, though... The auto heat system has been disconnected and all the flaps are open to let warm air in. There just doesn't seem to be any when it is below 70 degrees out. Plenty of air blowing thru the vent, just no heat.

[Josh D]

Change your oil temp sending unit. It's real easy. If it's the original, it's probably due.

[schumicat]

there are 2 oil thermostats. one internal on the back of the engine (controls flow the small cooler bolted to the lower right of engine) and an external one in right wheel well (controls flow to front trombone/radiator type oil cooler depending on model).

[na2ub]

The "flaps" on the heater boxes should be closed to allow warm air to the passenger compartment. Never heard of a 911 air-cooled engine running too cool. As long as it gets out of the "cool" zone, you should be fine. Sometimes this takes 10-15 minutes.

[Targa Time]

The engine oil temp. sender is downstream from the engine mounted oil cooler. So the temp reading you are getting reflects the efficiency of the cooler, not the temp of the engine oil after circulating through the engine. While rebuilding the engine on my 81 I cleaned a lot of dirt, bugs, maple seeds , etc., from the cooler vanes. And it did change the reading on the oil temp gauge. On a cool day, 60 deg., the temp gauge will struggle to hit 155-160 even though the oil tank is at 210.

[boyt911sc]

Originally Posted by Targa Time

The engine oil temp. sender is downstream from the engine mounted oil cooler. So the temp reading you are getting reflects the efficiency of the cooler, not the temp of the engine oil after circulating through the engine. While rebuilding the engine on my 81 I cleaned a lot of dirt, bugs, maple seeds , etc., from the cooler vanes. And it did change the reading on the oil temp gauge. On a cool day, 60 deg., the temp gauge will struggle to hit 155-160 even though the oil tank is at 210.

Targa Time,

Are you sure????? If the temperature sender & gauge are good and working, they will give you the oil temperature reading and has nothing to do with your engine cooler/s efficiency. The engine oil thermostat is closed when the circulating oil is below 176°F (+/-) and the auxiliary thermostat does come into play until the oil temperature hits 186°F (+/-) and higher. Where did you get this information? Thanks.

Tony

[Bill Verburg]

Originally Posted by boyt911sc

Targa Time,

Are you sure????? If the temperature sender & gauge are good and working, they will give you the oil temperature reading and has nothing to do with your engine cooler/s efficiency. The engine oil thermostat is closed when the circulating oil is below 176°F (+/-) and the auxiliary thermostat does come into play until the oil temperature hits 186°F (+/-) and higher. Where did you get this information? Thanks.

Tony

Both thermostats switch at the same temp because they are both the same design, using the melting point of wax as the mechanism for switching from open to closed and back.

there are essentially 2 parallel circuits, but the engine loop will warm first opening the engine mounted t-stat and directing oil to the engine mounted cooler, once this loop is up to temp then the outer loop can heat allowing the wheel well mounted t-sat to open directing oil to the front cooler. The dash gauge function follows the temp rise of the oil w/ 2 distinct plateaus and 2 distinct rises depending on ambient temps. If ambients are low enough only the first temp plateau is reached as the engine mounted cooler has enough capacity to keep the oil below the temp necessary to open the outer loop


the


964/993 of course have only 1 loop and function a bit differently

[Targa Time]

Maybe I have misdiagnosed the issue. However I did hot water test the thermostate, and replaced it just to be sure. Replaced the sender, tested the gauge and wiring. All seem to be functioning properly. On a 85 deg day I can reach 185 on the oil temp gauge. On a 60 deg day the highest temp to be reached is 155. Prior to the rebuild an 85 deg day would see an engine temp of 210 and a 60 deg day would result in a temp of 180. Am I missing something? When I rebuilt the engine to a 3.2 SS I assumed that the engine heat would increase.

[Josh D]

Originally Posted by Targa Time

Maybe I have misdiagnosed the issue. However I did hot water test the thermostate, and replaced it just to be sure. Replaced the sender, tested the gauge and wiring. All seem to be functioning properly. On a 85 deg day I can reach 185 on the oil temp gauge. On a 60 deg day the highest temp to be reached is 155. Prior to the rebuild an 85 deg day would see an engine temp of 210 and a 60 deg day would result in a temp of 180. Am I missing something? When I rebuilt the engine to a 3.2 SS I assumed that the engine heat would increase.

You changed the oil temp sending unit. This could be the difference in what you are seeing and the system is functioning normally.

The sending unit is just a thermocouple. The one you replaced probably saw thousands of heat cycles. They will degrade over time and give inaccurate readings. It's the first thing I would change when questioning accuracy of the oil temp after a visual inspection of the system (i.e. no crushed external oil lines). If you still have the old one you removed, re-install it and see if your baseline numbers change or stay the same.

[lindy 911]

You can also by a turkey thermometer and check the temperature of the oil after a drive. Put it in the oil tank neck while the engine is running.

[Targa Time]

Josh D
I changed the oil thermostate and sending unit only after running the engine for a few weeks and getting consistently low temp readings.
Lindy 911
Tried the turkey thermo and then double checked the temp with a Infrared thermo.
With dash gauge at 180
oil tank 217
Aux oil cooler 194
engine case at thermo 181
oil filter 208

With dash gauge at 150
oil tank 163
Aux oil cooler 128
engine case at sender 175
oil filter 207

And like I said previously, no matter how long I drive it at 60 deg the engine will not warm up anymore than stated.