I had a expansion tank  coolant level sensor blow out ofthe tank.Like a
rocket. My temp gauge had been highrer than normal,for a while. Well,I put
a new one  in and as a side effect, by temp gauge returned to normal.
Looking att he old one, I saw a crack in theplastic of one of the probes. I
dont know if thi swas because of the sensor blowing out ofthe tank. A cheap
fix.