'01 QC4x4 2500 V8 heating issue.

Air pocket in the system? Try starting it and idling for a while with the radiator cap off (block the radiator with some cardboard) until the thermostat opens up (upper hose will get real hot). After a couple of minutes after the thermostat opens, shut it down, top off the radiator, replace the cap, start back up, and see if the heat improves.

Done all that with the exception of blocking off the radiator. I do have more heat now but not quite as much as I remem- ber. No air in the system anymore...been purged out. With the temp I see being indicated...it seems the air coming out of the vents should be hotter.

Are both heater hoses approximately the same temperature? If not, you've still got a restriction in the heater core. If they are, then I'd say you've got a problem with the blend air door not opening all the way.

I'll check the hoses. Where is the blend door located?

Ok, checked the hoses and they are essentially the same temp. The return is only slightly "not as hot" which I think is correct seeing as how the core is basically a radiator and the coolant is slightly cooled as it passes thru.

Inside the HVAC box, which is behind the dash. It's not an easy job to get to it. Unfortunately, it sounds like you're down to that as the only other possibility (if you're really sure that it used to blow hotter than it is now).

After following this thread, I seem to lean towards your latter Tom. I have had several occaisions over the years where changing a thermostat has changed the heater temps slightly one way or the other. Just a very few degrees in the temperature that the thermostat opens/closes can translate to quite a bit from the heater. If the replacement is a slightly lower value, or just opens at a bit lower temperature it would be noticeable. I would say to try a thermostat maybe 10degs higher in value and just see if that makes a difference. The engine computer should compensate easily for such a small change as far as everything else goes. It's a shot, but at least a cheap one.......:-). If that isn't the problem, I agree the HVAC would be next.......and that ain't cheap.....or easy.

Ed

Might I suggest measuring the "actual" discharge temp of the HVAC system before proceeding further? Doesn't "seem" as warm is too subjective for me to warrant the time and expense of blend door surgery. Get a thermometer, measure the discharge temp and report back.

Mike

The controller for the blend door is on the underside. While its hard to get to with screwdrivers, its easier than removing the entire HVAC unit. Also, if you test the adjuster for the blend door and find no problem, it could be the blend door is somehow stuck. If that turns out to be your problem, I have experience on that too. You don't necessarily need to remove the HVAC unit.

That's the reason for the disclaimer at the end :^)

Already been thinking to do that. I have a digital thermo but needs new batteries. Will do this and report back.

Ain't this a grand 'ole newsgroup?

Awright, already!! I missed the disclaimer the first time.....

sheesh....

;^)

Mike

Ok, outside temp is 40-43 degrees, thermometer in upper vent indicates about 115 degrees. Brand new 195 degree thermostat.

Laz just for the hell of it, tape the thermometer to the heater hose and get an idea on what you have going into the truck

stupid question, but I have seen this scenario before: is the thermostat installed correctly? that is, is it installed with the spring towards the head? I did see one that was in backwards (spring towards radiator) and the end result was the same.

Are you talking about air temp coming from the upper vent? If so, what speed is the blower running at while giving this temperature? If you are expecting output air temps anywhere near 195, that just ain't gonna happen.

Will do Roy. Was thinking this AM of snagging a laser thermo in order to check the temps of each hose...core and radiator.

LOL....I'm not a DeeDeeDee....of course it's in correctly.

Yes, temp in upper vent. Fan on high. Not expecting temps that hot at all...just a little warmer than I'm getting.