Heat works good. I did notice (since this is an intermittent issue) that when the gauge wasn't working and the fans were on, the AC wouldn't work.
Heat works good both when the problem is occurring as well as when it's not? How good is good, aka duct temp? When the temp gauge reads low, the A/C likely doesn't work because the system doesn't know the difference between too hot or too cold, so again the failsafe is to think it's too hot thus turning the fans on and A/C off trying to keep the engine temp down.
Good thread. Just ran into this issue on my 2018 Regal GS with the 3.6. Sounds like a fun job to change the thermostat. I'll check to make sure the coolant temp sensor is reading a realistic number to rule that out and then go for the thermostat.
I ended up paying to have it done by local shop. They had to tear the top half of the motor to replace thermostat and temp sensor...
I found a fairly detailed youtube video on how to do the swap and I found a replacement thermostat for $120. I'm going to give it a shot and see what happens. Definitely an insanely overcomplicated design for a thermostat. At least if I ever feel crazy enough to bolt a supercharger on I'll know what I'm in for to do the swap haha
Sounds like Ford's better idea of putting the water pump inside the motor on their V-6 engines. That way, when it leaks, it takes the bearings and engine with it.. I think there was a class action lawsuit about that.
On the 86/87 Turbo 3.8 engines, there was a coolant fan delay relay that was activated by coolant temperature AND time after shut-off. That was the one relay that was not water-tight. GM instyalled the sensor directly in line with the hood-to-fender gap, with no protection for the relay. On the passenger side, those relays had a shield from the factory, plus those relays were water-tight. (At least SEMI- watertight, as they had a gob of that assembly 'goo' on the connector. That fan- delay-relay did NOT have any sealant, would get water inside, and the fan would come on after shut-down to activate the fan. The relay would fail and either allow the engine to overheat by NOT switching on the fans in operation, or would keep the fan on after shutdown acrtivation, draining your batytery. Naturally this was the most expensive relay on those cars, and unique to the 86/87 Turbo Regal and 89 Turbo Trans-Am...25527402.
Had same problem on daughter's 150,000 mile 2010 Ford Fusion. No codes; fan would run excessively after a drive even when not hot; eating batteries. I wasted no time in spending five minutes to replace the fan controller with a reliable brand aftermarket version (Ford doesn't make that controller but you could buy an entire fan assembly for a lot more money). Problem solved. Amusingly the VIN on car indicated an entirely different assembly should be found on the car.
