I need HELP! I am ready to give up. I have replaced the water pump, thermostat, flushed the coolant system, replaced the heater box and I still have luke warm heat. What else is there?. Both heater hoses going through the firewall are hot and still the heat sucks. The worst part is this is one of my snow plow trucks. Kinda hard to see when the defroster barely works. Any ideas would be awesome. Thanks

 

Do you know what temperature your coolant is getting to? The first thing we are going to have to figure out is whether the problem is getting the coolant hot or getting the heat transferred from the coolant to the cabin air.

 

The temp gauge is reading 190* I installed the 190* thermostat instead of the 180* to try and increase heat. Is there another way I should be reading the temperature to be sure it is getting hot or is the factory gauge pretty accurate? - Thanks

 

Similar problem. The heater core is warm, water is flowing thru it. I removed what I believe is the blend door motor (down on the pass side by the trans hump). I adjusted the temp cold/hot/cold/hot and the blend valve motor wouldn't turn. With the engine still running, I twisted/turned what I believe is the blend door and still no heat blowing from any of the vents. Does this mean the blend door is broken inside and requires dash removal? I think the HeaterTreater will fix but confirming now. Yep, I pulled it out and it's cracked on the inside.

 

Airlock in heater core?

Sounds like a blend door to me, but when they choke it is usually in the open position, which is full heat, not the other way around....

Could also be a vacuum leak at the switch, blend door actuator, or the vacuum connector under the hood at the rear of the engine hanging under firewall, debris in air inlet below cowl blocking airflow, etc...

 

Do you have access to a laser temperature gun? Those make figuring this out much easier.

The engine temp should be around 185*-190* and have been run long enough to get everything warm before accurately testing the heater. The heater line coming out of the head should be almost as hot as the engine temp, but maybe around 10* cooler. The heater core inlet should be about the same temp as the line by the cylinder head outlet. With the heater on and the fan on speed 1 the heater core outlet line should be close to the same temp as the inlet line temp. With the heater fan on speed 4 the outlet line will be considerably cooler and around 140*. If thats all correct then the air coming from the heater vent should be approximately between 140*-150*. If not then either the blend door is not working properly or the heater core is plugged up and not allowing enough coolant flowing through to offset the heat dissipation.

Also, with the glove box door off you can reach up and touch the heater core inlet and outlet copper section lines by hand. Feel their temperature and with a laser temp gun, measure them too.

 

For anybody else struggling with a heater core problem this article helped me resolve it within a day on my own https://www.thehubengine.com/common-...ems-solutions/. The article is on the 2003-2007 2500 but it worked on my sons 2002 2nd gen