I have a 2001 Elantra GLS. Yesterday while running errands, the AC began to blow warm air and the temp gauge went above half by a good bit. When the engine is cool, the AC works normally, but as the engine warms, so does the AC. I topped off the radiator yesterday with water (about 1 1/2 cups). Does the overfill need to be topped? Is the thermostat stuck closed? And is a little water going to hurt anything?