I have a new to me 02 QC 4.7 with 68000 miles. I just flushed coolant system, replaced therostat and refilled. I did this because when I towed my boat home from storage it was running hot and I figure it was due because previous owner never had it done. I then hooked up my boat and went for a drive. The temp gage never got much past halfway but when I turned on heat it was hot for 20 secs and then barely even warm after that. I tried to get all the air out by running with cap off till it got up to normal temp but never really noticed a "burp" then closed cap and bled from screw. Does it sound like maybe still air pocket, or got something lodged in heater core? Any help would be appreciated, Thanks.

 

an air pocket wouldnt cause that problem.its either a residual deposit thats blocked the heater core.what you should try is give it a couple minutes and turn the heater on again ,now if it sill blows hot for a short while then blows normal air,check the cable or vacuum line controling the block off vent to the heater core and if those work properly,then clean out the core.To do this,use CLR.remove both water hoses from each side which is located on the firewall,block them off,then pour CLR INTO THE CORE LINES ON BOTH SIDES,let it sit for a while,then flush it out with a hose,you must get all the CLR out.reconnect the water lines.and try the heater again.now if after you run the truck and it still doesnt give you hot air.YOURE SCREWED.

TRY IT,IT SHOULD SOLVE THE PROBLEM.

 

If cleaning out the core doesn't do the trick, you're gonna have to look at the controls. Sounds like the system is selecting a lower heat setting for you...? Mine isn't blowing nearly as warm as it used to, and I've noticed that I don't get much air from the dash vents. I haven't torn the dash apart yet to get to the mechanics of it, it looks like a PITA job.

 

I forgot to mention that the heat worked fine before pulling the the boat and almost overheating. Gonna try to flush out the heater core with the clr when i get home and see if it works. Thanks for the quick advise.