2003 Murano Heater Core Cold or Hot

[cocojoe]

I have a 2003 Murano. The heater will not warm up at idle. Will warm up after raising the idle up to 2500 But back to idle it will go cold. I had a Nissan shop remove an air bubble in the heater core and it stop for awhile but then it came back. They say air is getting into the heater core and it messes up the climate control. Now they are pointing to a head gasket. But I can drive this car alot miles and no bubbles in the overflow tank. No loss of fluids. Oil isn't milky. Now if it is a crack head gasket and air is comming into the heater core. Is there a sealer on the market I could try? (I don't like them.) Now I am 125 miles from the Nissan Dealer. I would like to find a fix I can do. I have alot of mechanical knownledge. Thanks Joe