Why is my temp guage going from normal to 3/4 and almost overheating? on 1994 Toyota Celica

When I'm driving my temp gauge will start to climb to about 3/4 or more but not fully overheat. Then I will put the heat on and it will drop back down to halfway which it normaly is always at. I checked my anitfreeze level and that's good. Radiator is newly relpaced. Is it my thermostat?

Asked by for the 1994 Toyota Celica
1 answer
ck coolant level to start with if good ck cooling fan operation