The water pump on my car went bad and caused the car to overheat recently. I had it replaced and also had the coolant replaced. Now I have a different problem with the temperature gauge that keeps fluctuating from the midline towards the red zone. I had the thermostat replaced but it keeps bouncing. I checked the coolant, oil, whether there are any leaks, the heater and it is all fine. Do you have any idea what could be the issue?
There are two possible scenarios to check out. First, if the cooling system was not bled properly to get all the air out, then the cooling gauge can fluctuate, as the sensor can’t measure the temperature of air/steam in the air pockets.
The other possibility is more serious. You probably blew a head gasket during the overheating episode, and the engine combustion is "super-heating" the cooling system rather than going out the exhaust pipe. I suggest enlisting the help of a local expert in order to inspect the potential causes for the thermostat problem and overheating issues. After proper diagnostics, they will be able to move forward with the appropriate repair.