[72nova434]

i have 05 duramax with heater issues.
when driving heater blows hot then cold gauges goes from 210 to 160 and starts blowing cold. upper radiator hose is cold also one side of the heater core is cold. ive changed out both t stats. used the bucket style filler with opening the bleeder on t sat housing after that system worked good while driving didnt over heat. blowing good heat out then i go to park it an let it sit for a couple of hours start it back up and it start all over again good heat then cold but it dont over heat . any ideas?

 

[Gdogg]

Try flushing the heater core with a water hose both ways. I have also filled the heater core with CLR for about 45 minutes then flushed it.

 

[jimmyz18]

put the cover on that goes over the grill....works great.

 

[prorat56]

How many miles? Head gaskets?

 

[JonnyT5]

Does it have automatic Climate control

 

[72nova434]

222,000 i runs like a champ oil level staying the same system hold pressure 16 psi for hours. i back flushed heater core it work good till i parked it over night started it up did good for about 45 min then wham o cold all over again

 

[72nova434]

Does it have automatic Climate control

nope

 

[72nova434]

after sitting for a while coolant level is on the half . i go to topp it off and open system it bubbles up to over flow then it reads full.

 

[72nova434]

ok did a head gasket test with the blue liquid and tester. showed no issues. any ideas?

 

[JonnyT5]

I want to say it has something to do with the dampener, like it is drawing outside air. My truck runs 160 and will run you out of the cab.

 

[Old Junk]

I want to say it has something to do with the dampener, like it is drawing outside air. My truck runs 160 and will run you out of the cab.

+1
Mine takes a long time to warm up, but with the grille cover on especially, it will get hotter than you can stand in the cab.

I would also check to see if heater control valve is operational, and concentrate more on the heater system/plenum