Early 1985 944 Cooling System Problems

chrsarcher · 07-02-2023, 06:26 PM

I've been having problems with my cooling system for a few days now on my early 1985 944. It started with overheating while stopped which was fixed with a new fan relay. But now, the fans do not spin at all until operating temp is reached where they both turn on full blast like the car is overheating (which it is not, the hoses feel like they're at operating temp). The fans do not turn off, even if the temperature drops below operating temp which I tested by putting a swamp cooler on full blast in front of the car. While the fans run, the fan relay gets dangerously close to overheating, I can barely touch it. When the car is turned off, the main drivers side fan spins slowly for a while like it should from the thermofan switch. Known good parts are the fan relay and fan speed resistor. My A/C relay is good, but looks different to any I could find, it only has 4 posts and seems to just turn the fans on full blast when the A/C is turned on; I've attached a photo of my fuse panel. My best guess is the thermofan switch is bad, but I am confused how the main fan would still work in slow speed after the car is turned off, but doesn't run in slow speed while the car is at operating temp. I am also unsure if both fans are supposed to turn on from the A/C relay. Let me know if anyone has had a similar experience and anything else to try while I'm waiting for a new thermofan switch.

944 Ecology · 07-03-2023, 12:29 AM

The proper cooling fan relay has 6 pins. The correct part number is 94461311302.

They are more expensive than a 4 pin relay, which might be why someone installed that instead. Fix that, and, who knows, your fans might start working properly...

v2rocket_aka944 · 07-03-2023, 03:18 AM

On the early car the fans only run at high speed when the ignition is on.
The slow speed option only happens when ignition is off but the water temp is high enough to trigger the fan switch.

The early fan switch only has one set of contacts; the difference is in the wiring. Ign on gives full switched 12V to the fan motors but still runs through the fan switch.

Ign off has battery 12V going through a big resistor to the fan motor, still grounding through the fan switch. The resistor is what makes the fan spin slow.

Only late cars have true high/low speed fans when the engine is running, because of a 2-position switch that still makes use of a resistor.

chrsarcher · 07-03-2023, 06:51 PM

So both fans are designed to run at full speed once temp is reached and have no slow speed setting while the car is on? Do they turn off and on depending on the temperature? Because my fans seem to always stay on once temp is reached. I'm worried that this constant current draw will burn out the relay; is it normal for these relays to get super hot? Also, my cooling fan relay does have six pins, it is the A/C relay I'm unsure about, even my fuse board only has 4 pins but every picture I see online they have 5 pins.

originalowner · 02:35 PM

FYI, the schematic, owner's manual, and workshop manual all disagree on the naming of these relays.

Position 3 of the fuse panel has a 4 pin relay. This drives the fresh air/heater fan motor. This relay is on anytime the ignition is on, unless starting, or the A/C is on. *

Position 1 of the fuse panel has a six pin relay. Ecology typo'd above, the correct number is 94461511302. This turns on one of the radiator fans, and bypasses the resistor for the other fan.

There is a different style 6 pin relay on the right side that turns on the other fan and the A/C control circuitry.

With the ignition on and idling, my engine slowly heats up to the / mark, then both fans come on and the engine quickly cools down to the \ mark, where they shut off.

* If the A.C is off, the fresh air fan is still running at fan switch position 0, it just runs real slow. If the fan bearings are shot, it can stall and the heat off the fan resistor will melt the plastic cover over it in the center back of the engine compartment.

v2rocket_aka944 · 07-06-2023, 03:13 AM

Quote:

Originally Posted by chrsarcher

So both fans are designed to run at full speed once temp is reached and have no slow speed setting while the car is on? Do they turn off and on depending on the temperature? Because my fans seem to always stay on once temp is reached. I'm worried that this constant current draw will burn out the relay; is it normal for these relays to get super hot? Also, my cooling fan relay does have six pins, it is the A/C relay I'm unsure about, even my fuse board only has 4 pins but every picture I see online they have 5 pins.

that is correct - both fans at full speed when ignition is on and the temp switch activates.

the relay does get hot.