Help needed - Crazy 968cooling system problem

[Shelby Wood]

Hello, I am stumped and would like to know if anyone else has experienced anything like this.

Our 1992 968 began overheating and acted like the thermostat was stuck so I ordered and installed a new thermostat. IE cold radiator, hot engine.

Car has always been very difficult to bleed but I have done it before and new how to jack it here, jack it there, ect. and get it bled. Know to have heater valve open, ect.

What the 968 does at this point.

When started the car begins warming up normally and at idle stays at proper temperature for several minutes. Then the temp starts rising very very slowly.

When the temp needle makes about the 3/4 mark the fans kick on and off for a few minutes once or twice.

After this the gauge temp continues to slowly climb. But the fans do not kick back on. The radiator is hot to touch but not as hot as the engine. The engine continues it's temperature climb slowly until we have to shut it down.

Hot, after shut down if I remove the bleed screw I get mostly steam. If I remove the radiator cap I get a rush of hot water, but nothing like you would expect from a car at operating temperature let alone one overheating.

Thinking that a head gasket leak might be pressurizing the system I have removed the bleed screw and rad cap with the engine running but get the same results, not extra pressure. No oil in the water and no water in the oil.

Also pulled the radiator to insure it was not blocked.

This problem is kicking my butt. Any help would be much appreciated.

[flash968]

did you test the thermostat before installation?

did you install the thermostat in the correct direction?

[idontknow]

Sounds more like the fans stop working after a few cycles but be sure the water's flowing through the system first. When hot and running, try to pinch off the upper radiator hose, if you can pinch it off without a pressure bulge, then skip the next part. Oh yeah, use gloves.

Did you check the thermoswitch on the radiator?

Do the same routine but attach a test light to the switch (pick a contact, either contact) and to a source of + power. The switch runs on - power btw. if the light comes on instantly, try the other contact. The test light should coincide with the fans running.

[flash968]

i was going to turn to the fan switch too, except for the difference in temps engine to radiator, and the bleeding problems

it the thermostat was verified and installed correctly, and there seems to be flow through the system, regardless of what the fans are doing, i would pull the plugs and take a look and a sniff, as well as take compression readings

[Shelby Wood]

Dumb question, but the 968 system is reverse flow right ? ie water pump pumps to the lower hose and engine gets cool, coolant from the upper.

The only reason I can't convince myself that this is a head gasket problem is that I had a similar but not a bad difficulty about a year ago. System finally bled itself and worked fine until now.

If I feel up inside the water pump to the little rubber seal the block off on the end of the thermostat seats against the edges of it feel roungh. Not pitted or with chunks missing, just rough. Could not getting a perfect seal here cause my problem??

Thanks,

[Shelby Wood]

Got it. But not sure how?

Had been trying to fix it without anti-freeze so that I didn't have to deal with it when draining. Decided I had been messing with it long enough that it might need some lube so added anti- freeze. Bled immediately and works perfect now?

Guessing that maybe the fluid changed enough to allow bleed? Belt quit slipping when water pump turned more freely? Beats me but then this was a very frustrating, time consuming project.

Thanks to those who offered advice,

[944 boy]

was it possible you didn't have enough fluid in there? If adding more fluid helped it could have been that simple. Were you adding more fluid after you let it cool down in between tests?

[flash968]

sometimes persistence is the answer

[JivenJim]

So Are you saying adding a new dash of antifreeze solved this? It doesn't seem to be to cause of the solution in my opinion. I just don't see how this would do it. Maybe you finally got the air bubble out cause this time you bleed it with out the car jacked??

I like to look for water circulating in the reserve tank right from the start up. The Reserve hose from the 968 Water pump and return line to the top of radiator should be mixing it up right from cold start up. You can see water swirling around through reserve plastic near hoses. This tells you pump is working even if thermostat still closed.

I've also had issues where the Gauge pod temp sensor gives false high readings cause the sensor contact is loose or corroded. And it's right under the bleed screw. Getting it wet from bleed will temporarily make better contact. Just throwing that out there.

[Shelby Wood]

I don't think I'll ever know what the problem was. But I am sure glad everything seems to work now !!!!!!

[bearone2]

you had air in it and it was low on fluid.
when it was hot and you saw steam from the bleed vent, it should have told you something.

you never mentioned if you had the heater valve open when bleeding.

[flash968]

yeah, he did - third paragraph

one thing about bleeding - the engine needs to be fully warmed up, beyond the thermostat setting, for it to work at all

also, in addition to the heater valve being open, the temp needs to be set to "high"

[bearone2]

thanks sheriff, glad you're on the job.