My truck has had a problem with the heater working poorly since I bought it. It has never been my only vehicle so I haven't addressed the issue.
The truck has a new cooling system (radiator,pump,hoses,thermostat) I also flushed the heater core from both lines. Good flow in both directions, no leaks. The temp adj (hot/cold) cable functions properly and moves the flapper in the heater box. The fan works correctly and blows through the vents, def, floor as chosen. If I let the truck idle and turn on the heat while sitting still, I can feel some heat from the vents, not much. However, going down the road it feels cool as the outside air.
Any ideas?

 

Check the hose coming off the water pump to the heater, it should be hot when the truck is up to operating temp. Is the operating temp of the cooling system at the right temp?

If the line to the heater from the water pump is hot then the other line should also be. Your thermostat is either busted, in wrong or the wrong temp. Make sure the thermostat is the right temp, don't put in a colder one because the computer relies on the temp being at a certain point.

 

Both hoses do get hot to the touch. I have run a myriad of thermostats from 160 to 197 degrees. The engine/cpu runs fine with with the cooler temps, however in an effort to solve this issue I have run overly hot thermostats. That made a minimal difference sitting still, but still no real heat.
The current stat is a 180 and keeps the temp a hair to the left of center on the factory guage, it works well in all weather conditions (AC on or off) with the HD aluminum radiator I added. It is not in wrong or busted. As I stated, the cooling system is all new, and I have run through all the basics. So I guess the next step is to pull the case.

 

If you have hot water going to the heater core and air is blowing thru it, the air WILL come out hot. How do you KNOW the blend door is working? Have you looked at it?

 

I haven't opened the case to check, however I checked the movement of the cable and the top of the blend door (crank) that it attaches to. It moves freely back and forth, the temp varies accordingly when ac is on, and I get a slight change in temp when the heat is switched on. It seems to be doing its job, however I haven't ruled out a problem in that area.

 

Hey Jimbo,

This applies to all of you who my have overheating problems.

Jimbo's problem may well be related to smething else that is causing the problem, however, since he mentioned hose changes, my comment may well appy to you as well Jimbo.

Especially if hoses have been changed or a new heater core installed.

A very common mistake that is often made with hoses and the heater core, is that the heater core hoses must go back on in the right order. Sometimes in the reassembly of the core and installing the hoses, the hoses will get put on wrong.

One hose goes to the water pump, the other to the block very near the thermostat. The heate core actually has one inlet and one outlet.

The hose from the water pump must go on the inlet side of the heater core, and the outlet side must go to the block.

Hook the hoses up wrong and you will get a reversed flow, that will suck cooled water away from the top of the engine.

Thus creating higher temperature readings, from the temperature sensor/sending unit, whatever, which is also, normally located somewheres near the themostat area.

Typically there are no "Which is Which" markings on the firewall, hoses, or outlets. After market repair manuals are vertually no help either.


It seems that there is nothing that says, which heater core pipe is which.

Thus, symptoms of overheating, high temp guage readings, unusually warm interior, in the front seat area, may indicated that the heater core hoses are on wrong.

The latter, warmer than normal front seat area, maybe hot air coming out of the dash vents, when the heater is not on, are sure signs of reversed hoses.

So, if you have changed out your heater core, or renewed the core hoses, and you have an overheating problem, try reversing the hoses.

If you don't see an immediate change, put the hoses back the way they were.

It doesn't cost anything to make this initial check first.

You might initially, check a friend, or even a stranger, for that matter, who has the same type car/truck, to see how their heater core hoses are routed.

Good Luck!!