Yukon XL No Heat

[bpopilek]

So yesterday my 2004 Yukon XL decided to start giving me fits right after it finally got extra cold and snowy here! I'm hoping someone could give me some advice. Here is what I've done and where I am at.

I noticed early on this fall that my water pump was leaking, so I replaced it. I also found that my truck only blew hot air while in motion, and cold air while it was stopped or at idle. At this point I replaced the thermostat and housing. I originally had the stock setup with the combined thermostat and housing. The new one is and updated GM version with the separate thermostat and housing assembly. Everything seemed to be ok until yesterday morning.

This is where my problem is now. Yesterday on my way to work, the message center said my coolant was too hot. The temp gauge showed the truck at about 250 degrees. My speed was only about 45mph and it was 6 degrees outside. I ended up parking the truck and looking at it after work. I found it was still doing the exact same thing. When I investigated further, I found that the upper radiator hose was hot, while the lower one coming out of the thermostat housing was cold. At this point I figured that I had a bad thermostat, and bought a replacement. I tested the old one on my stove top in a pan of water and found that it did actually open at about 175 degrees, so I'm not so sure it was bad now. With the new thermostat installed, the engine is no longer overheating and the temp stays around 235 while driving. However, I am back to the heater blowing cold air at idle and while stopped, and warm air while driving. In addition, the rear heater now only blows cold air, it never warms up.

Does anyone have any ideas of what could be causing this? Any suggestions on a repair? I am at a loss and would prefer to fix it myself instead of having to pay the dealership. Thanks for reading and for your thoughts.

[FishFind]

I am guessing you have air in the system or a clog in your heater core.

Mine did this yesterday after I changed the water pump. I had air stuck in the system.
Also I think 235 is still overheating. Most GM are 195.
I am guessing you have air stuck in the system.
They have a air bleed bolt by the thermostat that has a square head on it but I have never been able to loosen it.
You can disconnect the hose from the right side of your heater core and let the air out also.

They have a air bleed nut by the thermostat

[bpopilek]

I ended up having a bad gasket on the water pump which was leaking and allowing air to get into the system. Once I got it replaced everything was working correctly again. Thanks for the reply!