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Thanks Tom! This all makes sense. I have been verifying that the fans are on by cruising around my neighborhood and stopping to check. Agree they are hard to hear!
I pulled the radiator and I am attempting to fix the bunk Thermo fan switch threads. On top of the thread issue, the gasket that is held in with the tabs on the side of the rad started leaking not the first time I’ve had to do that. I have also tried to source a 71c thermostat but none of the usual 944 vendors have them so I orders a Mahle behr 80c to see if it’s more accurate. The wahler’s have been inconsistent with accurate opening temp the last 4 or so times I’ve ordered them.
Working on the leaks will update once I have one and will try no thermostat if the issue persists.
Thank you. I read through the whole thread and sounds eerily similar. I am still chasing the issue but one thing is for sure, the last 4 wahler thermostats are not opening anywhere close to where they are rated. Not sure this going on but quality control seems to be severely lacking..
I got super frustrated because no one seems to stock OEM 71c thermostats so I just went to the local parts store and bought a 71C Motorad thermostat that after testing it , *starts* to open at 74 and fully open by 79c or so. I am about to try this one with a small hole
Drilled in the top and a used OEM radiator because the threads are pretty wrecked on my current one. Just waiting on that in the mail. I will report back.
Replaced the radiator with a good used OEM unit. Pressure tested it at 15 psi for 30 minutes held great. No leaks. And no leaks in the entire system after install. Used 35% distilled water and water wetter
installed a 71C motorad thermostat. I tested it before installing it. It starts to open around 74 and It’s fully opening at 79°C. I tried ordering a OEM 71c but none of the 944 parts suppliers have them so I had to get this from O’reilly
installed 92°C Thermofan switch. Tested beforehand numerous times in boiling water. It opens closer to 97°C and closes right at 92°C. I actually installed the 85c first and the fabs never shut off once while running
I tried another spare fan relay I had and same issue.
Unfortunately, I’m still seeing the same behavior. The fans run even when driving around for 15-20 mins. The only difference is that the car is running very cool(at least that’s what the gauge says), assuming that’s because of the 71C thermostat. It goes very slightly above that first mark and that’s. The fans will shut off the first two or three cycles but that’s it. After that, I can’t get them to shut off until I turn the car off whether I am driving or idling. They will run for about 5-6 mins after the car is off and shut off. I have tried to bleed the system all day today. I drive around 35-40 mph for 15-20 minutes. Come to a stop fans are still running. So driving does not seem to help, so curious what that means. Restricted airflow? Crack the bleeder and no bubbles, just steady stream of coolant.
So why does the dash gauge stay very cool on the first line but the Thermofan switch that when I tested it, kicks on at 98c and off at 92c presumably stays above 92c because the radiator temp? So it seems like the temp where the thermofan switch is located in the radiator just isn’t stabilizing below 92c after the car is fully up to temp. Any other ideas? I will keep trying to bleed the system but not convinced it’s just that at this point. This behavior has persisted through so many iterations of different parts..
I guess I could try the grease fitting/clear tube method of bleeding the system but I’m just not convinced that will do anything. @Tom I know you mentioned to pull the thermostat and run it but shouldn’t having a lower rated thermostat that I know fully opens before 79c be a good test? Attached is a pic of where my gauge sits now which looks great but the fans just run and run and run! I’m very stumped. Wondering if the thermostat is actually too low? I thought the 85C thermofan switch would be a better fit but apparently not.
Sounds to me like you debunked the mismatched thermoswitch/thermostat theory, so I agree it's not worth trying the no t-stat idea now. I'm now curious is the fans are running via the a/c circuit. Does your a/c work? When the ac is on, the fan relay gets a signal to turn the fans on low. I'm wondering if that signal is either incorrectly stuck on (high, 12v) or if that portion of your fan relay isn't working right? Have you tried a new fan relay? It's a fairly complicated relay with plenty to go bad inside. (F9 makes a nive solid state replacement.) I have a foggy recollection that @chris white discovered this exact failure mode back during the Hoover Administration....?
If you've tried new/multiple relays and still have the issue, you might check pin A8 of the climate control unit. It should only have power when the a/c is on. I would think your a/c would be running if that power were stuck on, which is why I ask if your a/c works, but stranger things have happened...
Tom wrote: Fri Jun 26, 2026 3:35 pm
Sounds to me like you debunked the mismatched thermoswitch/thermostat theory, so I agree it's not worth trying the no t-stat idea now. I'm now curious is the fans are running via the a/c circuit. Does your a/c work? When the ac is on, the fan relay gets a signal to turn the fans on low. I'm wondering if that signal is either incorrectly stuck on (high, 12v) or if that portion of your fan relay isn't working right? Have you tried a new fan relay? It's a fairly complicated relay with plenty to go bad inside. (F9 makes a nive solid state replacement.) I have a foggy recollection that @chris white discovered this exact failure mode back during the Hoover Administration....?
If you've tried new/multiple relays and still have the issue, you might check pin A8 of the climate control unit. It should only have power when the a/c is on. I would think your a/c would be running if that power were stuck on, which is why I ask if your a/c works, but stranger things have happened...
@Tom It’s funny you ask about my AC. That’s next on my list to troubleshoot because no it does not work. Or at least the AC compressor does not kick on currently when the snowflake button is pressed. However, when I press the snowflake button, I do get low fan signal, and when I depress it goes off. Sidenote the snowflake light does not come on when I press it. Not sure if that means anything.
I guess if it was the AC stuck on wouldn’t the fans come on when I start the car or the ignition is on? Or is it possible that it’s stuck intermittently after the car is warmed up? Should I check pin 8 while the car is running on the climate control unit?
I have tried a spare fan relay. It seems to act the exact same way. I admittedly haven’t tried it for longer than than one fan cycle. other relay through the first two fan cycles were the fans actually do kickoff, so I’ll try that now.
Tom wrote: Fri Jun 26, 2026 3:35 pm
Sounds to me like you debunked the mismatched thermoswitch/thermostat theory, so I agree it's not worth trying the no t-stat idea now. I'm now curious is the fans are running via the a/c circuit. Does your a/c work? When the ac is on, the fan relay gets a signal to turn the fans on low. I'm wondering if that signal is either incorrectly stuck on (high, 12v) or if that portion of your fan relay isn't working right? Have you tried a new fan relay? It's a fairly complicated relay with plenty to go bad inside. (F9 makes a nive solid state replacement.) I have a foggy recollection that @chris white discovered this exact failure mode back during the Hoover Administration....?
If you've tried new/multiple relays and still have the issue, you might check pin A8 of the climate control unit. It should only have power when the a/c is on. I would think your a/c would be running if that power were stuck on, which is why I ask if your a/c works, but stranger things have happened...
@Tom It’s funny you ask about my AC. That’s next on my list to troubleshoot because no it does not work. Or at least the AC compressor does not kick on currently when the snowflake button is pressed. However, when I press the snowflake button, I do get low fan signal, and when I depress it goes off. Sidenote the snowflake light does not come on when I press it. Not sure if that means anything.
I guess if it was the AC stuck on wouldn’t the fans come on when I start the car or the ignition is on? Or is it possible that it’s stuck intermittently after the car is warmed up? Should I check pin 8 while the car is running on the climate control unit?
I have tried a spare fan relay. It seems to act the exact same way. I admittedly haven’t tried it for longer than than one fan cycle. other relay through the first two fan cycles were the fans actually do kickoff, so I’ll try that now.
When the fans are stuck on, can you get them to stop by depressing the a/c button and then releasing it? You still may have been close on the old thermoswitch/t-stat set up, so I'd recheck with a different relay for sure. You'd think the fans would just come on and stay on, but relays can take a while to heat up and get stuck. Or, if A8 is high all the time (and you don't realize it because the a/c doesn't work) then could cause your symptoms too. The climate control unit is no stranger to electrical glitches -- and perhaps something needs to heat up before A8 goes high. The dime store hack would be to just unplug the climate control unit altogether and see if the fans still refuse to shut off. The fancier way would be to tap into A8 and monitor it with a multimeter to see if by chance it goes high when the fans do -- if so, that would explain your fans...
not the first time I’ve had to do that. I have also tried to source a 71c thermostat but none of the usual 944 vendors have them so I orders a Mahle behr 80c to see if it’s more accurate. The wahler’s have been inconsistent with accurate opening temp the last 4 or so times I’ve ordered them. 
