papasmurf

I recently have got my early 944 on the road consistently after about 3+ years of resto/rehab and for the most part things have been running smoothly over the past few months. Last week I drove the car to church and had it get hot while sitting at a stop light briefly. Upon moving again, the temps dropped but again it got hot when I was traveling at slower speeds looking for a place to pull over and park it. Upon shut off it crept to the middle of the warning arc but I couldn't really use the heater as I would likely have had to keep the car running stationary which may have just made the problem worse. I noticed immediately that neither of the fans was running when they should have been. The car cooled off and I drove it home mostly without issue and the temps stayed just over half way on the gauge except when I stopped to get gas where they did creep up a bit while the engine was off and car not moving. I checked the fan relay last night per clarks garage and it is working, the fan fuses are both good, and though I have not tested the fans yet, I doubt they both failed at the same time. I drove the car at speed yesterday and the temps were fine and steady until I stopped for about a minute to see how fast it would get hot which did not take more than a minute or two. I pulled onto the highway again and the temps dropped below half really quickly, then rose to slightly over half and held pretty steady but the car would definitely get how at very low speeds. The car has a new waterpump, thermostat, hoses, belts, thermoswitch, etc. all with 500 miles or less of use. Some of the parts have been on the car for close to 3 years now but most of that time has been idle as I was only able to work on the car once or twice a week. I felt the hoses after parking it and the WP hose and the larger hose that runs across the block were hot...the skinnier hose that runs across the top of the radiator area below the nose panel was not seemingly as hot. The thermostat is a stant which I have heard rumors of them causing problems and with the way the temps were fluctuating it makes me wonder. I am still surprised that the fans seemed to quit working at pretty much the exact same time though. I had driven the car the night before the first time it got hot and it ran great with no signs of issues. The coolant system is full and has been bled a long time ago...I checked it again last night just to make sure though. The overflow tank cap seems to be fine too with no leaking coolant anywhere I can se....I did check the dipstick and oil filler cap in case of intermix and the car is not smoking.

931guru

There are a lot of reasons that your gauge is reading high. Don't panic. If the coolant is not boiling over (and maybe even if it is) you haven't overheated your engine. Get out a thermogun and start taking readings of the various areas of the cooling system to determine if you can identify a problem.

There is a really good writeup on the cooling system for an early car here:

https://newhillgarage.com/2018/02/04...tem-explained/

It's been unusually hot here and may be so there. The cooling system on your 944 depends on the difference in temperature between the coolant in the radiator and the ambient air getting sucked through the radiator in order te remove the unwanted heat. The gauge may be acting up (bad gauge, bad ground, etc.) The radiator may be clogged after 40 years. The thermostat may not be opening enough. The system may need to be bled. The gauge temp sensor may be faulty. The thermoswitch in the radiator may not be switching on the fans early enough. The fans might be getting weak....

As you can tell... lots of possibilities.

Funny how nobody ever complains about their car overheating in the winter months!

walfreyydo

https://www.clarks-garage.com/shop-manual/cool-01.htm
https://www.clarks-garage.com/shop-manual/ts-02.htm

Both fans stopped working at the same time is a big clue here and could be an issue with the fan relay, thermo temp switch, resistors. This is also the reason you overheat when the car isnt moving, but temp goes down when moving. The fans are what forces air over the radiator fins when the car isnt moving and keeps it cool. When the car is moving then airflow is restored without the need of fans.

Easy to test all of this, just follow the procedures. You didnt indicate the year of your car but there are differences between early/late and with a/c and without a/c, so pay attention to those differences and follow the procedure listed for the model you have.

papasmurf

The car is an early 85 (square dash). I had gone through clarks garage testing for the relay and it passed. Tonite I tested the fans by jumpering the thermofan switch and they operated as expected. I had to pull the dash cluster to replace an odometer gear that quit working so I measured the ohms of the resistor (I think there is just the one on early cars?) mounted behind the gauges while I was in there and it measured about 2.5 ohms which according to clarks garage and a few other places is higher than it should be (~1 ohm)?

walfreyydo

Did you test the thermo fan switch?

Resistors seem out of spec as you mentioned

orig944

You have enough evidence to conclude the thermofan switch is bad. Fan resistor is not used unless the engine is off, so not the problem. Thermostat and water pump working as shown by temperature drop while driving. Jumpering switch causes fans to run.