I noticed a couple of weeks ago when I'm trucking along and the heater is on the temp gauge will rise suddenly and then go back down just the same. I turn off the heater and it's solid as a rock right where it should be??? I turn the heater back on and it starts doing it again.
I checked the thermostat by waiting for the truck to warm up and feeling the upper hose and it seems to be opening as it should. I have recently changed over to an electrical fan, could that have something to do with it? I'm stuck and maybe overlooking something, have any of you guys had this happen to you?