ok so i just noticed that my burban will be running fine blowing hot air out of the heater and everything, then all the sudden it starts cooling down, so i glanced at the temp of the engine and it has shot up to 240ish it usually runs 190 area, so i keep looking at it then all the sudden it drops like a brick and the heater turns hot, what the hell? i was kinda thinking the thermostat what do you guys think?