I have a 2004 Dakota sxt 4x4 3.7L. I am having a heater issue inside the cab. The blend door works as well as the blower and resistor. I have coolant and both hoses to and from the heater core are hot. I flushed the heater core with water yesterday and the heat came back for a short time. I flushed it both ways and nothing came out but clean water. I then reconnected it and ran the truck with the radiator cap off until it started to come to temp then put the cap back on. The heat came back but was still not as hot as it used to be. What should I do? Full radiator flush and fill or could it be the thermostat or is the heater core bad?

 

Welcome to the forum.

Do you notice any temperature difference between the heater inlet/outlet hoses? The outlet should be cooler.

 

Thanks. Yes the outlet is slightly cooler. And I took out the glove box and visually inspected the blend door operating as I changed the settings on the controls.

 

There should be a pretty noticeable drop if there is enough airflow over it.
How does the airflow seem? Any chance of debris in the heater housing blocking airflow?

Maybe the heater core is partially obstructed.

 

I pulled it apart again and flushed it with water. Then I put some CLR in it and let it sent for 15 minutes. Then I flushed it both ways with water for about a total of 20 minutes. I just kept switching which hose I used to input the water. A bunch of black came out. I then blew out the heater core with air then water a few times. I then ran it with the coolant cap off until it got to temp and burped the system. The heat is now hotter than it has been in a long time. So for now it seems like this worked. Thanks.

 

I have the same issue and doing the flush only fixed the heat for a couple of days.

Maybe in a couple of weeks you can update us and let us know if the heater is still going strong.

I need to try the CLR to see if that fixes it. I have never gotten anything that looked too dirty come out.

How much do you think you put in?