ENGINE TEMP GAUGE MAXXED OUT IN 33 DEGREE TEMP.

AT NIGHT SEVERAL TIMES I WOULD BE SITTING AT A STOP LIGHT AND THE TEMP GAUGE WOULD GO FROM EXTREMELY COLD TO A MAXXED OUT HOT, WHILE BLOWING COLD AIR OUT OF THE HEATER. THE OUTSIDE TEMPERATURES WERE IN THE 20'S AND 30'S WHEN THIS HAPPENED SEVERAL TIMES