I have a 98 durango and the heater doesnt blow hot air. I've had it tested and they say it passes but just bearly. I've checked the hoses coming out of the firewall and the return hose is noticably cooler than the one going in. So I believe that its clogged. A friend of mine said there might be a silonoidthat lets hot coolant in that may be bad and not the heater core. Any suggestions?

 

Welcome to DF
Is the heater blowing warm or hot air when you are driving? If it is blowing hot air, my first guess is to look at aux pump on passenager side with heater hoses going to the pump.

 

Sounds like you need to blow out the heater core with a garden hose and the house pressure.

 

bearly warm air.

 

i agree with hydra, there is no control valve on the heater cores of these trucks