ok guys, my problem is that after my truck gets to operating temp, once in a while the temp will then drop and my heat quits. After that the temp skyrockets up to overheating and blows off the resevior lid off. About 20 seconds later the temp will come back down to normal operating temp.
I just put a new t-stat in because i thought that was the problem. Obviously thats not it.
I NEED to get this figured out!!

 

Try a new radiator cap.

Squeeze the lower hose while it's running at operating temp to see if it might be collapsing. Have someone rev it while you squeeze. Feel for soft spots. (I'd replace it)

Other than that, next guess would be water pump.


Had you done ANYTHING to the coolant system prior to this happening? (like a flush and coolant replacement?) If so, it could be an air bubble. You can leave a gap at the top of the hose where it attaches to the radiator to "burp" the air out (again, at operating temp, so the thermostat is opening, allowing full flow).

 

thanks for the quick help man! I will try these probably today becuase i cant keep driving my truck without fixing it.