so i was driving down a hill and the car was already warm and the tach showed it was at 1.5k but the car wasnt revving and i was in neutral...then about 10 minutes later...i was on a stop and the temperature shows the needle 3 bars from the "H"...then i start moving and it goes back to normal in the middle...and whenever i stop it does it again...i leave it off for about 2 hrs and try driving it again but now everythings normal...anyone know whats wrong?