911SC started running hot

[TibetanT]

Hello there:
My question has to do with 3.0L engine running hot and it appears this hot oil is not making the trip to the front trombone oil cooler. At times, I have checked the trombone oil cooler, and it is hot which is good, but yesterday my temp gauge was at 10 o'clock.
When I pulled into the garage to check the trombone cooler it did not feel hot at all. It was warm to touch.
In the past, when I started the car, I could hear the oil flowing through the oil lines going to the front of the car. Now, I do not.

So, my questions are:
1) what should I check first?
2) is there another issue causing this before oil reaches the Engine Oil Thermostat in the wheel well?
3) is it time to invest in a new Engine Oil Thermostat or does it need cleaning?


Thank you for all comments and help with this.

[Winter]

I'm not sure how you could hear the oil running through the lines to the trombone cooler upon start up. It is my understanding that the thermostat for the front cooler (trombone or otherwise) needs to see the oil get hot enough to route the oil to the front cooler, otherwise the oil is routed only through the engine. Happy to be corrected on this point, but I am pretty sure that's how the system works.

What is the gauge in your dash showing in terms of your oil temps?

The forum will probably need more data to assist in diagnosing what you are experiencing and to determine if you are having an issue or not.

[Mark Salvetti]

Ed,

I kind of agree with Tom. I didn't think there was flow to the front cooler until the oil was hot. But maybe the thermostat was stuck open, and now it is stuck closed.

Are the oil lines to and from the thermostat in the rear wheel well hot? They should be, until the thermostat opens to allow flow to the front cooler, it cycles oil to the oil tank. See this thread for how it works:
https://forums.pelicanparts.com/porsche-911-technical-forum/819049-wheel-well-mounted-oil-thermostat-flow.html

I'd be tempted to get the car back to operating temperature, and if the front oil cooler is still cool, give the thermostat some gentle taps to see if that will get the thermostat to open.

You may need to open it up (not easy!) and replace the internals, but I don't think these things go bad often.

Mark

[boyt911sc]

Ed,

You need to test and verify that the thermostats are both good and working. There are 2 thermostats:
a). Engine cooler thermostat.
b). Auxiliary cooler thermostat.

A simple water bath test will show how the slide valve/s react with temperature. Between 180°~190°F the normally open slot will start to close and the normally closed orifice will start to open. The open cross-sectional (A) + closed sectional area (B) = 100%. The slide valve is so designed to maintain constant total opened area to keep the uniform oil flow during the thermal transition.

If the test does not show 100% open to 100% closed, the thermostat is defective.

Tony

[TibetanT]

First and foremost, I appreciate this forum greatly!
Nice to have the brain trust that exists here providing excellent input.

Tom< correct, the system is NOT open when starting up.
I did think it was unusual that I would hear that flow at times at start up with windows up.

(But maybe the thermostat was stuck open, and now it is stuck closed).
Have to agree with you on the second point, that it is NOW STUCK.

Mark
As far as the Temperature gauge, this car came with the red bar at the top so no way to tell actual temp. The gauge was reading just around 10 o'clock which is just below the "Red bar" area of the gauge. I pulled over to let her cool down some before returning home to the garage.

Tony, I will take these items apart and do the testing you suggested.

Will update you all with my findings soon.

Thank you!

[TibetanT]

Mark: Forgot to mention that, yes, both oil lines were hot going to the Aux.
I am going to try what you suggested and tap on the Aux Thermo to see if the front oil trombone gets warm after doing so.

I have heard that the oil temp gauge has numbers scribed on the side, so will check that to see if I can determine the actual temperature. As mentioned, just below the red bar is where my temperature needle was before pulling over to cool down.

BTW...does anybody know if the Aux Thermo requires a "special" tool to open for access?

[Mark Salvetti]

Originally Posted by TibetanT

Mark: Forgot to mention that, yes, both oil lines were hot going to the Aux.
I am going to try what you suggested and tap on the Aux Thermo to see if the front oil trombone gets warm after doing so.

I have heard that the oil temp gauge has numbers scribed on the side, so will check that to see if I can determine the actual temperature. As mentioned, just below the red bar is where my temperature needle was before pulling over to cool down.

BTW...does anybody know if the Aux Thermo requires a "special" tool to open for access?

If you look under the left side of the temperature gauge from the right, you should be able to see temperature markings in degrees Celsius.

The thermostat cap has a big slot in it. You need a drag link socket of the right size, but it may still not budge. You don't want to put a lot of force on it without holding the thermostat, or you could crack the connections to the oil lines.

Mark

[A930Rocket]

[silverlock]

[TibetanT]

Thank you for all the information and pictures posted regarding the Oil Temperature gauge.

Tom and Mark, the oil temperature gauge needle was just above the 120 degrees Celsius mark. (Glad I pulled over to cool her down).

Last night, I got the car to operating temperature and put my hands on the Front Trombone cooler which did not appear to be even warm.
Next, I tapped gently on the Aux Thermostat and waited a couple minutes.
Using my mechanics stethoscope, listened to the Trombone pipes and heard a vague sound of oil moving, a trickle at most.

Waited for about 10 minutes, tapped gently on Aux Thermostat again, then put my hands on the Front Trombone cooler. This time it was hot to touch. Again, using the mechanic's stethoscope I could hear lots of oil moving through the pipes.

So, I believe a replacement of the internal thermostat within the Aux Thermostat will do the trick. Thoughts?

Also, going to save some $$ and invest in the Carrera cooler replacing the trombone. (Modine or PMO)
Anyone have recommendations as far as this idea and all the parts needed?

As always, "thank you" for your help!

[kltarga72]

Use a laser thermometer to see exactly how hot your oil is, maybe dash guage is faulty. Test the engine oil cooler, oil lines with the laser thermometer. Know what you have before tearing into the external thermostsat.
Make sure a mouse hasn't built a nest on top of the cylinders and near the engine oil cooler. You need both cooling units to maintain normal temperature. The engine oil cooler is the primary unit.
I still have the trombone cooler on my 1980 SC and it works fine.
I had to replace my external thermostat a few years back because when removing it I damaged the threads on it so be careful. I believe you can still purchase a rebuild kit for it.

[TibetanT]

Thanks, Lash !

Appreciate your comments and advise. Working very slowly so I do not break anything important.

[Winter]

Ed - yeah, 120C is too hot!

Seems like you’re on track to sort it, good.

My ‘76 has the Carrera front cooler and I consistently run at 210F/99C under load and on hot days here in Colorado.

Of course, my 2.7 has all the other mods done (fan upgrade, no thermal reactors, etc.) to address heat. But I’m thinking that I may also install a puller fan to compliment the front air scoop in the bumper that the PO installed for the front cooler to preemptively deal with anything hotter than what I am seeing. Cheap insurance.

[Mark Salvetti]

Originally Posted by TibetanT

Waited for about 10 minutes, tapped gently on Aux Thermostat again, then put my hands on the Front Trombone cooler. This time it was hot to touch. Again, using the mechanic's stethoscope I could hear lots of oil moving through the pipes.

So, I believe a replacement of the internal thermostat within the Aux Thermostat will do the trick. Thoughts?

Also, going to save some $$ and invest in the Carrera cooler replacing the trombone. (Modine or PMO)
Anyone have recommendations as far as this idea and all the parts needed?

As always, "thank you" for your help!

I had no idea if the tapping was going to work, glad it did. Let us know how you make out removing the cap to get the thermostat out. I would try that before trying to undo the four threaded fittings to get the unit to the bench. First thing I would do is the drag link socket. If the cap doesn't budge and you have an air hammer, I would get a cheap Harbor Freight ratchet (because you are going to sacrifice it), attach the drag link socket, and hit the handle of the ratchet with the air hammer while trying to turn the cap. The vibration will probably loosen it.

You might be able to grab the cap with a pipe wrench and turn it, but that will apply a lot of force that can damage the thermostat.

Adding the Carrera cooler is not plug and play. You need to install the bottom support bracket and a connection to the back of the headlight bucket. Check out these threads, they are for the 28-tube cooler but I think the Carrera cooler install is the same:
https://forums.pelicanparts.com/porsche-911-technical-forum/1016696-us-83-sc-trombone-28-tube-cooler-mounting.html
https://forums.pelicanparts.com/porsche-911-technical-forum/1163178-am-i-last-guy-planet.html

Mark