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Discussion Starter · #1 ·
Hi, I am having some issues with the 2003 4.7 Ram I just bought. The cabin heater literally does not work under any fan speed. It will blow warm for maybe 5-6 seconds the first time you turn the fan on...but will blow completely cold after that.

What also happens...is my engine will overheat if I try to drive on the highway for about 20 miles. Just driving around town, the coolant temps seem to be okay, but if I start driving 60 mph for an extended period of time, the engine will progressively overheat until it almost gets to into the red.

I checked the hoses going into my heater coil, and one of the hoses seems to stay cold.

Could this just be an AIR BUBBLE? I don't really know what steps to take to properly diagnose this issue...but I installed a new radiator cap and bought a new thermostat.

Could anyone help me find where the thermostat and heater control valve is on my truck?
 

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If your return hose is cold then your heater core is blocked up. You could try back flushing the heater core to see if that takes care of your problem. There are chemicals you can try to help break up the really bad clogs, that may or may not work. Worst case scenario, new heater core. I'm having the same issue myself but I have to wait for a break in my work schedule to take care of mine. Good luck with yours.
Don
 

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An air bubble can cause this. Try this:
2 heater hoses run along side the passenger side valve cover. There is a "T" here. Unclamp the hoses and blow air through on of the to clear the funky coolant and scale out. Pour some mean green or similar in and let it sit for an hour or so. Then flush with clean water both ways until the water runs out clear. Reconnect hoses.

Once you change the thermostat and flush the heater core, refill the reservoir and park the truck with the nose as far up as possible. Leave the radiator cap off and run the truck until the thermostat opens. Repeat at least once more and see where that leaves you.

The other scenario that would cause this is a blown head gasket, but try the simple stuff first before jumping to conclusions.

Oh, and the only heater control valve to my knowledge is the knob on the dash that you turn to the red. This moves a door in the hvac box to seal off the a/c condenser and open the heater core compartment. There is no valve that shuts off coolant to the core though. Coolant is always running through the core.
 

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Discussion Starter · #5 ·
I just want to say thanks to everyone that helped me out in this thread. I did everything you guys suggested.

The good news...My heater core works now. I flushed a ton of nasty orange crud out of my heater core. It flowed clean water both ways through the core when I reconnected the hoses.

I also replaced my thermostat, and "burped" the system as best as I could.

The Bad news, I took it out for a long drive after I got done, (started out my drive @ 200F*) it only took about 3 miles for the coolant temp to start to rise into the 220+ range. By the time I got it home 10 minutes later, the needle was almost pegged out.

I just don't get it...There is no sign of air in the system, I have no coolant leaks, thermostat is brand new, heater core flows... Why am I overheating so badly????


P.S. When I was inspecting my coolant in my drain pan, I found small specks of metal sitting at the bottom of the pan...what does that indicate...water pump...?
 

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Discussion Starter · #6 · (Edited)
Well...I replaced my radiator...problem solved.

The only indication I had that the radiator was bad...is the engine got hotter the faster I drove. Which is backwards to how it works with a good radiator.

There were no leaks.
 
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