Weirdest thing. Replaced the radiator on Tuesday and everything appeared OK. Several heat up cool down cycles later, I notice that if I rev it (in the driveway or on the road) over about 2500 RPM, it will very quickly cool down. Temp guage isn't graduated but I'm guessing from about 200 degrees down to maybe 130. Heater blows noticably cooler also. Getting ready for a trip, weather is cold. Only things I can think of are air bubble in engine, head gasket making bubble in engine, or a thermostat in backwards. I haven't touched the thermostat and never noticed this before.

Out of desperation, I changed the thermostat (buried on a 4.2L in 15 degree weather), and it fixed it. Thermostat was in the right way, I've never seen one fail other than just stick.

What fixed this truck, did I just inadvertantly remove an air bubble that was stubborn? I'm baffled.

Mark Cantrell