Hey guys i need some help figuring out why my truck overheats. It only happens about one time for every tank of gas, so about once every 200 miles. What happens is, it gets to operating temp fine and out of nowhere my heat will blow cold. Next the temp guage will drop and seconds later it skyrockets up to overheating and blows the overflow lid off and makes a huge mess. By the time i try to pull off the road and shut it off, the temp drops back down to normal operating temp. Im stumped!
I have replaced the radiator cap and thermostat with no luck. I have also bled the air out of the system and it has fresh coolant in it. The hoses look good and it still has the factory waterpump and radiator.

I noticed that the overflow tank does NOT have a vent, so the system is not vented at all and that doesnt seem right to me?
Anyway i need help!
Thanks!!!!

 

sounds like you have an air pocket in the system and it works it's way out. Bad thing is that you dont know how the air pocket got in there and you have been running with the airpocket in the heads. I hope you have caught it in time to prevent a warped head or blown gasket.

 

yea i have really no clue on how to cure it. The truck runs/idles fine and the oil is not mixed with antifreeze so im pretty sure it hasnt done any serious damage yet.
thanks for the help