2002 Mitsubishi Montero

The car temp gage jumps all over we have changed the thermostat flushed the radiator both sending units and heater control valve the gage still jumps all over will peak up to the H but come down very quick have touched the top of the radiator and both hoses and not real hot also the radiator is not bubbly over or into the resorvior I have run out of ideas any chance it could be just a bad gage