After a long drive I finally checked my oil cooler temperatures. The oil cooler was at an average of 70 C with the crosspipe temperature around 98 C.
Doug Hillary's average oil cooler temp was 76 C with a maximum of 88 C.
It APPEARS that my oil cooler may not be doing its job. I'll install a new oil cooler thermostat and see what happens.

 

That would be very interesting, been looking at the wrong culpret all along.

 

Ernest,
Interesting! - Looking forward to hear 'the final answer'

 

I would find it surprising if the total lack of an oil cooler caused the engine to overheat. (but good luck)

 

Hi,
Ernest - to assist you, my current temperature readings are;

Oil Cooler:
Top hose average 74C
Top hose max 88C
Top hose min 55C

Bottom hose average 75C
Bottom hose max 90C
Bottom hose min 59C

Engine:
Vee/VC average 88C
Vee/VC max 90C
Vee/VC min 85C

I cannot recall what you have done with your car's oil cooler since the radiator change, is it still acting as an intercooler-heat exchanger or is it mounted remote from the radiator?
Are you still using a 75C coolant thermostat?

As with all components of the 928's integrated "cooling system" ( coolant, oil, air flow ), the oil cooler temps are quite meaningless in isolation. The 928's oil cooler thermostat opens at 87C and it is possible that it will remain closed for long periods of vehicle use. It will depend mostly on the prevailing ambient and the vehicle's use. Racing or events driving is another story!

It is noted that Porsche's oil pressure readings for the 928 are at 80C using their recommended oil viscosities. This may indicate that this is about the oil's "normal" core temperature ( core = the stabilised temperature of the oil in the sump ) when the engine is not being driven too "hard". With hard driving the temperature will of course be higher

As in most vehicles, it appears that the oil's core temperature will operate at about 5C to15C above coolant temperature most of the time when the engine is fully warmed up and oil pressure has assumed its normal position at idle ( indicating that the oil's temperature has stabilised )

Core oil temperature needs to be regularly above about 76C to ensure the eradication of the normal products of combustion

In my experience oil coolers will usually reduce the oil's temperature or stabilise it very quickly once the oil thermostat opens and if air flow is good. They typically "cycle" and rarely remain fully open for long periods in normal use. Oil type and viscosity can play a role in its final operating temperature too

I don't believe you have told us what type, brand and viscosity of the oil you use

I hope this helps

Regards

 

Hi Doug,
The 91 has an external oil cooler separate from the radiator. It appears to be two tubes running along the "floor" of the nose of the car in front of the AC condensor.
I'm using Castrol Syntec 10W50. I still have the 75C thermostat, but since it made no difference (as we both expected) I'll be replacing it with a proper 83C one.
I'd like to stress the fact that the engine temperature was indicated at about 90C when I took the readings from the cooler lines. By your description I'd expect some flow through the cooler at that coolant temperature.
Would you expect temperatures taken from the surface of the oil pan to be meaningful? They MIGHT be helpful in determining the expected state of the oil thermostat.
I'll be replacing the oil thermostat and both springs within the next few weeks and we'll see whether it makes a difference.

 

Ernest. I have a good feeling about this. I'll put money down that it will drop your temp. Reno

 

Hi Ernest,
I suggest you try to get some temp. readings off the oil pan as a starting point. These will indeed give a "core" oil temperature indication.
Any readings should be a "clean" ones and tried a few times to see if there is much variance. Remember that with the volumn of oil in these cars it does take some time for the oil temp. to stabilise

Then you should gather both "in" and "out" readings at the cooler. If you can trace the hoses back and try to get a clean reading closer to the block
this will be another indicator too

It may be that so far you have not read the cooler with the thermostat open. When open the in/out variance should be about 10C-15C but I cannot be sure

My median readings both in and out of the cooler have been the same at 75C - not far from your reading(S). This probably indicates that the cooler is not open often in my car and probaly not in yours either!.
The intercooler aspect of mine will likely give a higher reading than your car which is open to airflow. This will tend to cycle the flow more often when needed in your case

The oil you are using - 10w-50 - will tend to run at the higher end of the oil temp scale. Porsche's spec. for reading oil pressure in your model car is in an oil temp range of 80C-100C, this is a good nornal oil temp range indicator.
I do not know when your oil thermostat opens but it is still probably still at the original 87C

Regards



Regards

 

Very interesting! I thought about you during our Saturday fun drive in temperatures in the 90ies. No matter what I did, the indicator never even got close to the last white line.

Just for curiosity: Where is the thermostat for the oil cooler located?

I hope this will solve your problem and allow you to sleep better in the future!

 

Nicole;
Just above the oil pressure sensor

 

ErnestSw - what are the part numbers for the springs?

You said the 'regulator' was 928 107 172 01 (Pelican states as superceded by 928 107 172 02).

Nicole - the thermostat (regulator) is highlighted here:

 

Hi Porken,
The parts from top to bottom are

928 107 171 01 spring
928 107 172 01 regulator
928 107 173 00 spring

The numbers are the same for all years.
HTH

 

ErnestSw - thanks very much. Any problem sourcing the parts?

Since we change all the other bi-metal/wax bulb sensors, switches, and thermostats occasionally, I wonder why this part has not been referred to as a wear item?

 

Hi,
I just ordered the parts from Zims and was told they should be here tomorrow. We'll see.
I've spoken to a couple of the big three and to the people at Zims and noone can remember replacing these parts.
I'm either breaking new ground in the eternal search for the answer to the overheating problem, or barking up the wrong tree. In any case, the total for the parts is about $50.00 and worth the effort.

 

Porken: Thanks for the info!

Ernest: Are you telling us on a public message board that you are not supporting the "Big Three" with your parts orders?