Hi all,

I was close to home when I suddenly saw my temp gauge climb to the red. I thought maybe this was due to my radiator fan resistor bc I hooked up my scanner and noticed the fan didn’t come on at 221. I soldered a new resistor in and just went for a spin with my scanner connected this time. I didn’t sit at idle to check if it came on at 221. I just took off. Same thing happened where the temp gauge went up to red. I was right around 195F when this happened and the temp was bouncing chaotically from -40 to 70, to 80, to -40, to 180, etc. Could this be the thermostat? It’s only about three years old, 10k on it.


Just returning from the quick spin, with the key turned to on position, the temp gauge is at red and the temp is a steady -40F

 

That sounds like a wonky temp sensor, doesn’t it?

 

i forgot to mention I did a clutch job and the coolant temp sensor snapped but everything stayed in place. I got a new one to swap out but the miles I have driven haven’t given me any problems so far. There was one time the cel came on and it was bc it unplugged slightly so I fastened down in the meantime before doing the sensor swap and didn’t have any other problems. But to be fair maybe it’s dead now for one reason or another so it’s worth changing.

along with the relatively new thermostat, the water pump also has only about 10k. When I’ve refilled the coolant, I’ve used the bleeder screws and I’ve also used a power bleeder to ensure there’s no air. I understand a leak could cause a lower boiling point bc of a pressure drop, and I don’t appear to have any. I’ve checked with dye. People here know better than I do, but I don’t see how the fluctuations would be related if it were something like a leak. If it were more of a radiator fan issue than just the resistor, I also don’t see how it would be related. I would think in a case like that, the temp would rise and not drop and then the temp gauge would spike to red, and I would see the steady climb on my scanner.

the sporadic illogical temp changes make me think it’s something electrical like the coolant temp sensor.

 

It was the coolant temp!!! Silly of me to think it would only be a problem if the CEL was on. It had come unplugged. As I mentioned, the sensor snapped but only its black housing. It’s the fork like prongs that connect to the wiring are there and its black cracked housing is stuck on the wiring. It’s really ghetto right, but unless it slips out I’m okay in the meantime. Def plan on swapping. It’s just been rough with the weather.

Thanks for inspiring me to have a look!

 

check your coolant level? I had a leak at the pump gasket and would have similar swings when low (think sensor hitting hot vapor and then hitting fluid)

edit:
just saw you would get cold temps as well, sounds like a sensor (mine would go from nominal to hot).