Why is it that when ever you go to sell a car it decides to break? I put it in the truck trader this weekend and tonight it acted up. The problem is that its got a 4.3 with a chip and 170 degree thermostat. It usually runs in right around 150-170. Tonight i went to go get gas and everything was fine, drove about a mile and the heater was working fine and the gauge was at its normal spot. Just before I got to my house on the way back i noticed the gauge was at 220! I know thats not outragouse but when its never run above 170 before, even with a heavy load, it scared the crap out of me. I parked it and started checking it out. Theres a small leak on the lower rad house, i watched it for 30 seconds and the drop never fell from the hose, with the engine running. Now the wierdest part of the whole deal is that the heater quit blowing hot air. It worked on the way to gas but not on the way back. WTF. Any sugestions would be appreciated since its going in the truck trader on thurs. Oh yea, and at idle it jumps from 220-180 spuratically, no noise from the belts or water pump.