Disconnect the hoses and put a garden hose on it to try to flush it out.

 

Thermostat in backwards?

 

Electric fans (or clutch fan?) working properly?

 

Electric fans work perfect. If I bypass the heater core for the week just so I can drive the truck and get the removal tool for the hoses will that hurt the engine?

 

As long as it is not still overheating, you won't hurt anything doing that.

 

Update, I flushed the heater core and got my heat back. Unfortunately the truck is still overheating after I drive for 7 minutes. Popped the hood to find it broke thru the bottom of the reservoir this morning spitting out fluid. I'm beyond stumped at this point.

 

Blown head gasket?

 

^^^^ this.

 

A buddy suggested get a new reservoir with a new cap since it is a pressure release one. I did see when I installed the new radiator it said put a new cap in but I didn't want to take another ride to the store. Could that cap really cause that much of an issue?

 

Radiator or reservoir caps don't cause engines to overheat. They just help prevent them from boiling over as quickly by controlling the pressure in the system. If your engine is overheating it's going to boil over at some point anyway. A new cap won't hurt but it's not going to prevent the coolant temperature from going to high.

 

Okay I’m having a similar problem and have no clue what it is. There’s no leaks. My water pump and heater core are good. Just put a new thermostat in. Just put a new fan clutch in. All of the sudden there was no heat in cabin and the engine was overheating. I read the forum and I was wondering why you poured coolant into the radiator hose instead of the reservoir and how that worked for you. Could my system be air locked?

 

I have a 2004 Silverado 5.3L