Hi Everyone.
I'm, a retired firefighter from the Seattle area, new on the Forum although I've read and learned quite a bit here. I recently bought a 2003 Dodge Ram 1500 Quad, 4x4, 4.7L, Automatic, 88,000mi.

I'm having trouble with the heater. It was working intermittently, blowing cold air then nice and hot, then back to cold. Now air barely gets warm. If I have the blower on high, the air is cold, if I turn the blower on the lowest setting I get slightly warm air. Doesn't matter which direction I point the air, ...floor, defrost, dash, it's all the same. Engine is not overheating, runs just a notch below center on the gauge.

Here's what I've done so far. I removed the heater hoses about halfway between engine and firewall where there was some existing couplings, and flushed the heater core forward and backward with hot water. The flow was good and unrestricted in both directions, I got just a bit of rust/sediment for a couple seconds, then clear water. I hooked the hoses back up and installed a Prestone access tee from their flush kit. I did a complete flush and coolant change and replaced the thermostat with an OEM 195 Stat. The old coolant was very clean with hardly any rust or sediment so I didn't use any cleaner. Put everything back together, added fresh coolant checking for leaks. Left the bleeder plug loose while I ran the engine for about 20-30min. and got some bubbles for the first 10 minutes or so before they quit. Still no Heat in the cab!
While running, with the engine hot, I checked the upper radiator hose and it was hot, the lower radiator hose was cool to barely warm.
Anyone got an idea what the problem is? Sure could use some help on this one!

 

Check the hoses going to/from the heater core, the inlet side should be HOT to the touch, outlet side might be slightly cooler. If those seem ok, I would take a look at the blend door. (temp door.) Not sure how it is controlled on the 3rd gens, but, the later 2nd gens used a little stepper motor, and the coupler liked to break, and give exactly these symptoms.

 

Thanks,
I'll check tomorrow when I have some light!

 

with the t stat change maybe you still got air in system? I changed my 03 to cap on radiator and traditional overflow. so it will be different from your set up. What I do is raise front end of truck start engine with rad cap removed and blower motor on high once engine gets to operating temp rev engine (2000rpm) till heat comes out defrost. top up coolant and recheck coolant level again after next cool down cycle.
If positive all air is out do like mentioned start looking at blend doors.

 

HeyYou,
I checked the hoses when I got home this afternoon and both were hot but like you said one was a bit hotter than the other. Thing is, it was my first drive after the coolant/thermostat change and interestingly enough, after a while the heater started working. I could feel really hot air coming out on low fan so changed it to high fan to see what would happen and it stayed hot. Will follow up on this...

 

Hey Big Guy,
Thanks for the advice!
Seems to be blowing hot for now. We'll see how long it lasts. You may be right, I may have air in there somewhere so my next step is to follow your advice and purge the system. I'll follow up and let you know what happens.

 

If you have good heat now it will not go back to having an issue your flush job of the core just took time but once it started to get good flow you are now good. I read a lot about the blend door being an issue but that logically can only come into play when you have good in and out flow temperatures as you do now.

 

Thanks everyone for your help and advice, it seems my problem is solved.
I've driven it 4 days in a row now and the heater is still blowing hot each trip. At this point I'm thinking there may have been an air bubble in there somewhere. I did the job in my driveway which had a steep downward angle to it so the nose of the truck was lower than the rear. After I actually took it out on level ground and drove it, the heater started working. It blows correctly thru all the designated vents and will heat me out of the cab if I don't turn it down.
As for the initial problem, I think it may have been the T-stat. I put the old one in simmering water and it just barely opened so it was probably sticking. I'm surprised the engine didn't overheat though. I wasn't driving it very far, maybe 5-10 miles so maybe the cool weather we're having was enough to keep the temp normal?? ...Anyway it seems to be working properly now. I've searched around and learned a lot about my new cooling system. This is a great Forum!
This thread got me thinking about that blend door. Is there anything I can do to extend it's life as far as maintenance, or maybe the way I use the heater?

I love this truck! It's my 5th Ram, starting with a '76 Ramcharger. They've all given me great service, no complaints whatsoever, I hope my luck holds out with this one.