Hi all.
I am admitting I am needing some help. lol It will be appreciated - it is cold now!
My 02 with a transplanted 360 slowly developed this condition. The heat only blows hot when the motor is revving or cruising.
Now I thought this was a easily diagnosed condition...and Ill admit it is driving me a little crazy, so some clarity would help too...
Here is what I have observed...
Coolant is full. I have tried to burp it a few times. The temperature of the motor is even. Vaccum is 19 at idle and very smooth. The motor runs excellent and is getting the correct gas mileage. No check engine light.
So I looked and test what I can concerning all the vacuum lines. All good.
The old head unit, being in Florida most of its life, was worn and cracked when I took it out. There was also no more clicking between modes. So I changed it out with a nice used one from Seattle I put it in and the vents work flawlessly. Fan works great and cold/heat works, but for the heat to work, it needs to be revved. I replaced the check valve and lines on top of the motor and checked to see if other things like the fresh air valve were working. It all seems great.
I have replaced the heater control valves too. Ive noticed that Elk used Four Seasons ones.
Nothing has changed with all of this work. It still works the same...
Any ideas...Im stuck...thanks.

 

With the engine warmed to operating temperature, check the hoses to the firewall. There will be two going to the heater core. Are they both hot? It is tight in there. If both hoses are hot, you may have a defective heater control device. (I'm not sure how your vehicle is equipped.) If one hose is hot and one cool, your heater core may be partially blocked.

 

I have front and rear heat...I think this set up is a little different...
Here is what I have...it feels like the upper hose isnt getting any coolant.

..i can sqeeze it...is this just a case of not enough coolant, but if it is, how the heck do I get more in when the whole system is full and keeps a constant level?

 

It's possible you have an air lock bubble. Those can be stinkers to get out. However, I would first make sure the control valves are working. You can try opening one of the hoses at the rear heater core. Withuot being there in person, I can only guess.

 

Thanks...Yea I should see how much coolant actually is making up into the core.
It really does seem like an air bubble. It sure is strange...

 

It's been so long since I worked on a van with rear air, especially a Dodge, I'm not sure how your rear core is set up.Can you get to it fairly easy? Does it have rubber hoses with some room to work? Is it a high point or is the front core higher? I'm thinking you MIGHT be able to add a flush port with a cap to the rear hose and get the air out that way. However, I hesitate to suggest it since I'm not sure how your lines are routed.

 

It was too rainy to work on it today...
Ill post the line routing when it stops snowing/raining/snowing/raining LOL

 

Spring?

 

Finally figured out what was wrong. The heater hoses were backwards. That would do it.
The heat now will cook you.
Im not sure how I fed that up, but I took pics so if anyone wonders how the hoses are supposed to be with rear heat, I can post it for you.