Hey guys I am a long time reader, but I have never posted. I have owned my truck for around 6 months and I love it. I have been having some heat problems though. It's a 2002 Ram 4X4 4.7L. At first the heater was only blowing luke warm air on the passenger side and cool air on the driver side. I thought it might be a blend door issue, so I checked them out and they are working fine. Next I changed the thermostat, overflow cap, and flushed the heater core with a water hose. A big rusty glob of stuff blew out of the heater core when I flushed it and after that I got a good clean flow of water. I figured this was my problem so I filled it back up with antifreeze, bled the system and the heat was blazing hot. Both hoses on the heater core were equally hot now. I thought I fixed it, but no. Whenever I started driving the truck the air would get cooler and cooler and when I would rev the motor the heat would come back, but as soon as I get off the gas and let it idle it gets cool again. After the truck has sat for a little while when I first drive it when I get on the gas I hear a bunch of liquid gurgling in the heater core, but it stops after a couple of minutes.

I have a ton of heat when the overflow cap is off and the system isn’t pressurized, but as soon as i put the cap back on and drive it the air turns cool. It warms up when the engine revs. I have no other symptoms, but I thought it could be a leaking head gasket pushing cylinder pressure into the system, so I pressure tested it and had no leaks. I am starting to get sick of not having heat. The water pump shows no signs of being bad, could the water pump be the problem? I hate to go to the trouble of changing it and pay the money for a new pump if that isn't the problem. Could I still have air in the system? I have spent around 3 or 4 hours with the truck running, the radiator cap off, and working the bleed screw to get the air out. At first a bunch of bubbles would come out from around the bleed screw now its just coolant. One thing that throws me off is with both thermostats the level of coolant in the overflow tank always stays at the same level. I figured when the thermostat opened I would lose a little coolant in the tank, but the coolant level never moves. I know its working because the motor doesnt overheat and it warms up pretty quick. I don’t know what else to do, but it sucks having awesome heat and then losing it when the system builds pressure.

 

I would check the heater core again.. Might have dislodged something with the flush and it clogged again..

 

I thought the same thing, so I unhooked everything and flushed it again and got a good flow of clear water. It could still be the heater core, but I don't think it is because I get awesome heat when the system isnt pressurized.

 

it sounds like a bad thermostat to me. I have had the same problem before going through multiple thermostats before one works proper. i would also run some descaler through the system to make sure all the crud is out.

 

Dodgeboy, thanks for writing in. If it was a faulty thermostat wouldn't the truck overheat or not heat up quick enough. I have put 2 thermostats in so far and nothing different has happened. Could this explain why its not letting air out of the system. I don't understand why my fluid level never moves? Does anybody else have any ideas? I really want to fix this lack of heat!!

 

not necessaritly, sometime they will open sporadically at what ever temp sometime they are just slightly stuck open ans allow a little coolant past etc... I would still flush with a good descaler, mount a new thermostat and burp the system real good.

 

I recently had the same problem. A water flush doesnt always work. Try this, an acid flush. Writeup is on the last page.
https://dodgeforum.com/forum/3rd-gen...ats-wrong.html