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dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

After cleaning the contacts of the low speed fan resistor, my cooling fan would come on when my temperature was below the second mark and the engine was off. The fan would NOT come on when the engine was running. It only runs a few minutes. I've replaced the temperature switch ( 77/83C), relay and fuse. Is there a circuit for the turbo that I am missing which uses another tenp sensor?

Thanks,

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Alex Roy · Posted: Sun Mar 16, 2003 8:52 am Post subject:

Your fan is supposed to go on after you turn the car off. While the car is running, it should only come on if you are sitting in traffic and your temp is over maybe 2/3 hot. When you turn off the engine, you get "heat soak" and the temp of the coolant rises because it isn't circulating, that is why the fan goes on after you turn the engine off.....it is supposed to.

Remember that your engine temp sensor is in the head, and the fan temp switch is in the radiator, so they ARE getting the temp from 2 different places.

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

As I understand it, the fan only uses the temp switch in the radiator. I can understand the temp sensor on the head getting heat soaked but it doesn't control the fan (or does it?). Also, when the engine is off and the fan is running, I can turn the ignition switch to on and the fan stops. I can then start the engine and the fan stays off. Shouldn't it stay on until cool down?

Thanks,

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Alex Roy · Posted: Sun Mar 16, 2003 9:16 am Post subject:

yes, it should stay on in that situation. I'd suspect your ignition switch or a relay or something of that nature.

924 turbo · Posted: Mon Mar 17, 2003 12:26 am Post subject:

I'm a little confused. Does the fan work while the car is running? Does it just not come on until a higher temperature?

If your fan is running (ignition off) and then you switch the key to the on position, it should start running faster.

Alex is probably right that it's the relay or some other wiring problem.
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Jon Furst

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

The fan hasn't started when the engine was running, just immediately after I shut it off. By the gauge (which appears to be working alright) it has never gotten hot enough to kick the high speed circuit on. One other thing I noticed yesterday evening is, when the fan is running (switch off) the temp gauge pegs to the right (even with a cold engine). Beginning to think that a PPO (not Bob) has done some innovative electrical mods.

Thanks,

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Zuffen · Posted: Mon Mar 17, 2003 11:09 am Post subject:

Dennis that is a gremlin, I cunning little gremlin.....

I'll ponder this one....

ask Tom for advice too

Initially I think there is a ground problem....
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Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Bob,

Today, while changing the O2 sensor and trying to find the oil leak, I noticed the primary (drivers side) fan plug was pulled out about 3/16". That could explain the gremlin. I would also bet it also has a higher temp thermostat than fan switch (77/83C).

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Zuffen · Posted: Mon Mar 17, 2003 2:40 pm Post subject:

There is a chance I might have changed out the switch or thermostat to a to improve the heat transfer. Oddly all my 931s have always run on the cold side. The summer is the real test.
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Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951

numbbers · Posted: Tue Mar 18, 2003 11:23 am Post subject:

Bobby, if you have 931's that run cold, I need the secret. Mine always runs hot in traffic.
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1980 924 Turbo

Zuffen · Posted: Tue Mar 18, 2003 11:38 am Post subject:

I spend 35 minutes burping mine when I change coolant or do any work where the collant has to be removed.

I've forgotten so much not working on my car....she just keeps tickng
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Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951

numbbers · Posted: Wed Mar 19, 2003 10:57 am Post subject:

Yeah, I always bleed the hell out of it with the front end raised. But I still peg the guage on hot days in stop and go traffic. That is with the heavy duty Performance Radiator and the low temp fan switch and thermostat. I have thought about trying an aftermarket fan. Anybody had good luck with one?
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1980 924 Turbo

Smoothie · Posted: Wed Mar 19, 2003 11:16 am Post subject:

In a couple days, I might have some info on fitting an aftermarket fan, but if you already have 2 and they both work, I'd look into activating the right-side (AC fan) off the left fans' circuit via a relay. Currently, if you turn on the AC to start up the right-side fan, do your temps drop to an acceptable range?
(I still need to verify whether the AC fan ever comes on to supplement the regular cooling fan while the AC is turned off.)
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Zuffen · Posted: Wed Mar 19, 2003 2:12 pm Post subject:

how do you know your actually too hot? you might buy or borrow a infrared gun and the next time your pegged give the radiator a shot and check the hoses, etc.

The electrics might be wacked. The temp sensor is in the water housing on the back of the head I believe. I've noticed those 10mm bolts can get crudy and there the only thing actually making contact with the head as the housing sits on a gasket. Maybe you have too much resistance from the sensor. the brass end and the connector might need a good cleaning . Even the sensor sometimes need to be pulled and cleaned. I think they are NPT threads and brass so they don't require sealant. Check that with the factory manual before believing me as I'm not sure.
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Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951

porschetroy · Joined: 30 Dec 2002 Posts: 32 Location: Sacramento

Dennis,

I had a similar in my '82 931 where the gauge would flicker and peg "hot" when it was actually cold. My "gremlin" turned out to be the foil on the firewall insulator. It was rubbing the temperature switch at the back of the head and grounding it - sometimes. You might want to check that out. -Troy