My 98Ram 1500 will blowslightly warmer air (but not hot air) when adjusting the temp control **** to full temp. Historically (not sure how long) I have been able to hear water moving back and forth between the heater core and the engine compartment. That has stopped. The temp guage is is the normal position and reaches that position in the normal amount of time which is about 3-5 mins in 45 degree weather. Suggestions on trouble-shooting the problem would be appreciated.

 

Is the air hot when you turn **** to max ?

 

fill ther radiator while reving the motor and put the cap back on on high idle to force coolant into the heater core i had the same problem just had to bleed it out good it would be slightly warm with the fan on low and when u turned the fan on high it would be warm and then cool right off due to lack of curculation

 

then the heater started blowing lukewarm air in my 93 dakota, a suggested fix was unhooking the heater core lines from the motor, then running water from a garden hose through the heater core backwards for a few minutes to get the crud out of there. worked back then on that truck, heater started blowing scalding hot air out again, you could give it a try.

 

Just fixed the same problem in my wifes Durango yesterday. Flush the heater core out. Actually backflush it. Unhook the hose at the water pump and hook a water hose there. Then connect a drain hose to the other heater hose That goes into the intake manifold and flush it into a bucket to see what comes out. Took about 12-15 gallons of brown gunk water before it was clear. Heater works fine now....actually better than ever. Only takes 20 mins if that.

 

There is never any hot air.......cold air when set to blue area.........slightly warmer air when set to red....