overheating mystery

[Browzer52]

Time to ask for help...........1986 930....temp guage reads 210 after about 15 minutes @ 50mph (80 kph) may climb slightly but does not drop.Oil filter casing temp is 220 according to my temp gun.Have changed the engine thermostat,added a return line oil cooler @ reservoir,have removed cooler from engine,flushed and installed new seals,fresh oil and filter.Thermostat in right rear fender is working as cooler in right front fender is hot,as are both cooler pipes although temp differs between the two,which it should.Air temp today is about 70,not hot enough to affect engine temp,Am I missing something here?Any input would be appreciated.

[DRACO A5OG]

Was the new thermostat properly rated to move at specific temp?

[SchnellSchweitz]

I know my wheel-well thermostat was not working properly and it drove my temps up. I believe at least one of your pipes should be very similar temp all the way to the cooler. If it remains quite a bit cooler, even after a long drive, I'd suspect this thermostat. They do get stuck and need to be replaced.

[Browzer52]

Ordered from our host a new thermostat,there was only one available for this engine,unlike a water cooled nothh american engine where several are available.

[Browzer52]

Both pipes were hot,one considerably more than the other which leads me to believe that this thermostat is working as it should.

[SchnellSchweitz]

This may not relate to your issue, but keep in mind that vacuum leaks also make your temps go up. If you have any burbles at idle I'd certainly hunt those down and eliminate them while you wait for your new thermostat. By the way, there is an alternative thermostat. It's made by Mocal.

BAT, Inc. - MOCAL Oil Coolers

Just keep that in mind for future reference....

[wrinkledpants]

How is the foam seal around the oil cooler in the fender?

[fanaudical]

Any blockage on the cooling fins on the cylinders? Have you looked under the engine shroud?

[Browzer52]

Originally Posted by SchnellSchweitz

This may not relate to your issue, but keep in mind that vacuum leaks also make your temps go up. If you have any burbles at idle I'd certainly hunt those down and eliminate them while you wait for your new thermostat. By the way, there is an alternative thermostat. It's made by Mocal.

BAT, Inc. - MOCAL Oil Coolers

Just keep that in mind for future reference....

All vacuum lines are new,will keep the Mocal in mind,do they offer an engine thermostat as well?

[Browzer52]

Originally Posted by wrinkledpants

How is the foam seal around the oil cooler in the fender?

Foam around fender cooler is as well new.

[Browzer52]

Nothing living under the shroud,did check this.

[boyt911sc]

Inspect and test the auxiliary thermostat for its opening temperature. Below is an example of the thermostats in different condition at same operating temperature.



The left most thermostat is stuck closed (defective), the middle thermostat is partially open, and the right most thermostat (good) is fully open at 186°F (water bath).

So you could see from these thermostats how a good thermostat operates versus the two (2) other thermostats causing overheating in 911 engines.

Tony

[Steve@Rennsport]

JHMO, but do NOT use the Mocal thermostat on a 911 engine since it doesn't have the pressure relief valve that the Porsche factory one has.

That does two things: protects the front cooler from being blown out from cold (thick) oil and bypasses un-cooled oil back to the tank during periods of high demand (sustained high RPM) by the pump.

The Mocal units are OK on other engines that do not have as good an oiling system as the dry-sump 911 one already has.

This surely isn't a good place to save money.

[SchnellSchweitz]

Go with what Steve says.... he knows more than me by a mile!

[Browzer52]

Originally Posted by boyt911sc

Inspect and test the auxiliary thermostat for its opening temperature. Below is an example of the thermostats in different condition at same operating temperature.



The left most thermostat is stuck closed (defective), the middle thermostat is partially open, and the right most thermostat (good) is fully open at 186°F (water bath).

So you could see from these thermostats how a good thermostat operates versus the two (2) other thermostats causing overheating in 911 engines.

Tony

Thanks Tony,this is the only component I have yet to address physically as the two forward oil lines differed in temp leading me to think that it is working properly.Should it be only be opening partially this would restrict oil flow and likely would be the source of my problem.When I get the time to deal with this will do so and let you know how it worked out.
Regards

[boyt911sc]

Bowzer,

Not until you have tested and verified the operation of your auxiliary thermostat, you are doing guess-work or hoping it is in good condition!!!! This may not be the root cause of your over-heating problem but the auxiliary thermostat is a very common cause of over-heating. Rather than assuming it is not the culprit, I suggest that you test it and eliminate it from the list of possible culprits. If the test shows it is good, then you have eliminated one variable in the equation. Then check the other variables.

Tony

[Browzer52]

Originally Posted by boyt911sc

Bowzer,

Not until you have tested and verified the operation of your auxiliary thermostat, you are doing guess-work or hoping it is in good condition!!!! This may not be the root cause of your over-heating problem but the auxiliary thermostat is a very common cause of over-heating. Rather than assuming it is not the culprit, I suggest that you test it and eliminate it from the list of possible culprits. If the test shows it is good, then you have eliminated one variable in the equation. Then check the other variables.

Tony

Have checked everything else physically.Found the original engine thermostat opened slowly and not completely in a pot of boiling water so replaced it.Engine still running hot although not as hot as it was.Will remove and check the external thermostat.Quite possible I have more than one contributor to my problem,car is an 86,although low mile,most parts are original.
Regards

[Browzer52]

Update for those who are interested.......removed aux thermostat,disassembled and replaced internals with a tested core.ran the car into town and watched temp run up to just under 210 then quickly drop off to about 180,climb again to just over the 210 mark and hold.Activated the cooler fan (manually activated by a switch on my console)and watched the temp drop and sit at just under 210.Thinking that the thermostat slug may be hanging up in the housing bore.Will disassemble and check for this next time I get spare hour or so..............the quest continues

[Browzer52]

Next.............removed and disassembled thermostat again.Had a good look at the housing bore and noted a few rough spots and the fact that the slug had wiggle room.Decided to assemble and install the trermostat without the slug thinking that this would allow free flow to the front cooler verifying the thermostat as my problem source.WRONG.............seems that the slug is required to direct oil to the cooler regardless.Eight miles saw the temp reading 210+ and the cooler pipes ice cold.Trial and error.Will be ordering a new thermostat this afternoon.

[Jdub]

Thank you for following up on this topic.