Warm heat, but not hot...Need Advise

[Funkadelic]

I have a 2003 Ram 1500 with the 4.7L. After engine temp warms up (gauge reads just a hair below middle line between C & H), I get warn heat out the vents, but not hot. Certainly not hot enough to stay toasty warm in Iowa in winter. Been like this for a few years now. Last fall I replaced a bunch of stuff...took out dash, replaced a few blend doors that had broken tabs and replaced heater core and AC evap core while I was in there. Also replaced the thermostat.

Thought I might have some air in the system still, so worked on the bleeder screw where the top radiator hose goes into the block, then also got it up to temp and ran a bit with the radiator cap off. Still no change in the heat.

What am I missing? What else would be keeping hot coolant to pass through the heater core? Or hotter coolant to pass through?

 

[Snake15eyes1998]

Mine started doing this about 8 months ago. After about 15-20 min of driving. I start to get hot air. But until then, its just warm. But on my passager side vents, its always hot. Its just my driver side vents I have the warm air then hot after 15-20. I'm thinking it's a blend door not opening all the way. I would think it's the same problem your having. Or your HVAC controller is bad. Its not really going to hot, but staying in the middle

 

[rule18]

I had that problem in a couple of Wranglers, turned out to be a clog in the hose (once the upper, once the lower) so a flush was the fix. Can't say if that's your issue.

 

[Funkadelic]

I previously had the issue where it was warm on the passenger side and fairly cold on driver's side. After I fixed the middle blend doors, I now get consistent warm air from both sides. Just not hot.

 

[Funkadelic]

Any other suggestions from the group? Not sure where to look next on this truck.

 

[shadowhawk]

on my Pontiac, I had the crappy dexcool antifreeze. I had to have the heater core REVERSE flushed to get heat back in it. Might be worth a go.

 

[Oliver Closehauf]

So very first thing is I see there is a calibration procedure that you need the DRBIII scan tool for. You may just need to do that and the rest below is garbage.


Next thing I would try and find out is if my heater core is getting hot. I have a multimeter with a temp probe (physically touch) and IR mode (Point it at something and read the temp).

I'd see if I can compare the core VS the radiator. Point is to see if it's a coolant flow problem or not. Don't mix measurement methods. You want to know the difference as much as the actual exterior temp.

You may only be able to get to the inlet/outlet pipes coming through the firewall. I'd measure them both, but without any blower running. Then turn the fan on high, wait a couple minutes and re-measure. Write everything down. The numbers may point to the problem.

Measure close to the inlet and outlet on the radiator.


Next or alternatively, you could hook up a hose to the outlet of the heater core and test the actual flow. Plug the return hose or get a length of clear hose and put it in between the heater hose and return line of the core. Just want to see the flow. It doesn't have to get hot. Just run it long enough to know your core has good flow.

Once you know it's not a heater core issue you know you have a blend problem. Guess that is where I would finally go buy that endoscope I've always wanted to get. See if I can use it to look at the door position.