2006 3500 4X4 dually SLT blows cold air even after engine is warm until some amount of driving at highway speeds, then begins blowing hot air. Also seems that the overhead outside temp reading does not adjust until the heat is flowing into the cab. This past weekend, the engine temp guage showed redline even though there was no way the engine was overheated and then after running about 45mph everything settled back down to realistic readings. I think these are all related, but don't know why. Any thoughts before I end up stuck in the cold with no defrost?

 

I would say you have a stuck thermostat and/or bad water pump. You should be getting some heat after 5 mins on highway. Low antifreeze could also be the problem as a air pocket can delay the thermostat from opening. Just some thoughts. Check your over flow is there anything in it?

 

Antifreeze level is down some, not empty, but I am adding and going to run the truck and refill as needed as a first/easiest fix. If not, I am thinking thermostat also. Consensus seems to be a Cummins stat or nothing. Thanx for the response.

 

Loose clamp and cut in short piece of radiator hose near block caused air to enter system and kill the heat and freak the eng temp. Fixed now, Thanx

 

great good to hear you got it fixed.