CDT944

I have been fighting a cooling problem on my '87 944 NA for a couple of weeks now. Quick background, radiator, thermostat, water pump one year old and thermo fan sensor new. It believe I was vented properly. It never actually over heats it just gets to the upper range mark and stops. The strange thing is if I keep the heater control to all hot it is fine. As soon as I turn it off (to cool) it immediately heats up and moves to the upper mark. Turn heat control back to hot and it comes back down. It seems like the heater issue should be some sort of a clear indicator but I don't know enough about the cooling system to know what it means. Bad thermostat? Any suggestions?

Thanks for the help...

Chris
'87 944 NA
Austin, TX

Airflite40

Are your fans coming on when it get hots? Have you checked the coolant level?

CDT944

Yes the fans are coming on. I did the test from clark's to test the relay and the fans came on when they were supposed to and I have verified that the fans are coming on when running. Coolant level is good.

Spidey944

Have you tried bleeding the cooling system while running the heater? It's poss. that an air pocket is causing your high temp readings.

CDT944

I had the heater in the full hot position during the venting. I guess I am going to try and vent again. I believe clarks says to vent, drive the car and vent again.

Airflite40

Did you jack up the pass side as high as possible when venting the coolant?

I have had good results with that method, heat on full blast, jack pass side up, the point is to get the bleeder screw as high as possible, higher than the reservoir.

CDT944

I jacked up both sides, driver and passenger. Am I suppose to only jack up the passenger? This is the strangest thing, If the heater is full on it is perfect, as soon as I turn the heater off it slowly climbs to the top mark and stops. When i turn the heater on it immediately starts to fall and settles in the proper place. I can do this off/on over and over again with the same results. So the consensus is it is a vent issue not thermostat?

Chris
'87 944 NA
Austin, TX

Cone_eater

You have fluid flowing so the thermostat is not an issue. I vented mine while the car was flat. I have perfect results after having the same issue.

pjburges

The heater core is a radiator in itself, so with its small added assistance you are running back in range. I would definetly say your first bet is to bleed the coolant system as the others have stated. Is your car stock in the front end? That lower engine cover helps to create a negative pressure pocket in the engine bay and pull air through the radiatior, and the engine runs cooler with it. Im in SA right now or Id come by and show you how to bleed it real quick.

CDT944

The front end is stock. I tend to agree it is a vent issue. The probem doesn't seem progress steadily. What I mean is, the car will warm to normal operating temp and maybe run fine for a ways after then start with the problem. Last night on the way home, 15 minute drive on freeway, it was fine. Other times it may just progressively go to the top mark.

Chris
'87 944 NA
Austin, TX

Reimu

I had to vent, vent, and vent again and nothing.

IMO, the best way is to jack up the passenger side, and wipe off the coolant tank opening. With your arm open the bleeder screw slightly, and blow in the coolant tank... and when you run out of that breath screw it back on tight. You'll have to do this a few times, and refill the tank when it empties. You'll hear it bubble through and eventually coolant will spurt from the screw. And thats it, you're done... You can bleed normally after this too but I found it not to be neccesary, I have had no problems with it whatsoever.

Cone_eater

They make a system pressurizer for about $30 at local part stores. They prevent you from having to get that delicious taste in your mouth. It makes it easy. Pressurize and bleed then done!

CDT944

I am going to call around tomorrow and see if any of the auto parts stores have loaners, if not I may just pick one up because if I got to go thru this everytime I need to drop some coolant to do work I'll go crazy.

Chris
'87 944 NA
Austin, TX

Cone_eater

No stores have loaners. I thought I would save you the hassle.

Clint's 944

Autozone will loan you just about everything in their store. I've borrowed pressure testers, spring compressors and even odd sized sockets that I know I'll use once.