I have two good mechanics stumped on this. At 315000 miles I took my truck to a good mechanic to change the head gasket per instructions from the Dodge dealer. He had the head totally rebuilt at this time and installed a Cummins head gasket. This truck works hard, normally pulling a backhoe or something similar. About 10000 miles after this work, I noticed an occasional problem with the heater not blowing very hot air. Some time later, the truck pegged the temp gauge. I pulled off and raised the hood. It was a cool day but the radiator was blowing cold air and the valve cover was cool to the touch. The thermostat housing was hot, but I could still hold my hand on it for a few seconds. It was pushing water out of the reservoir. After it sat for a while, I removed the radiator cap and started it. It would push a bubble up every 4 or 5 seconds. A second mechanic( the original guy was sick at this time) thought the head gasket was blown, so he replaced it. He also pulled the water pump and checked it but ruled that out. The truck continued to get hot after about 20 minutes of drive time. It would climb slowly to 210 and then after about 5 minutes would jump to 245. He pulled the head again and sent it to be checked. It was a little warped and was planed. The amount was very minimal but they planed it anyway. The mechanic checked the cylinders as much as he could but there is nothing obvious. Head was reinstalled and he had me take it home to see what it did. It took quite a while for it to reach 210, then it quickly dropped back to around 180, It repeated this several times on the 20 minute drive home but it never got any hotter. The heater still was just blowing lukewarm air even when it was running at 210. I pulled the radiator cap with it running, There was some pressure, but not much. It was again pushing bubbles but more of them and at a consistent pace. We are all at a loss. Any suggestions would be appreciated.

 

Test the coolant for combustion gases first. See what that turns up.

 

Thanks Hey you. I will ask him to do that.