Why does Temp light comes on but not 2 days in a row changed water pump thermostat and coolant why does car run hot one day and not the next 93 olds. cutlass?

By changing the water pump, you may have allowed air to enter the engines water passages. In order to get rid of it you must allow the engine to burp out the air by adding in coolant while engine is running. Make sure you do this method when the car is cold. In the mean time your temp gage might read hot until the air escapes the engine. If it does not read hot any more then your problem is cured. Good luck.