16 389 glider with 12.7 no heat

Not yet, truck had to take a load. Hoping when it comes back I can get the oil cooler off. Thats about where I am at. The water pump I originally took off this truck actually just got put onto another truck and it has no heat issues so I know that wasnt the issue at all.

 

Update. Truck finally came back. Removed the oil cooler housing and it was clear and oil cooler was clear. Put new oil cooler in as had it here. Ran truck and still no heat even after thermostat opened up. Thought it had an air pocket in it still. Opened the cap and there was alot of pressure in cooling system. Put gauge on it and it built up 15 psi in about 15 min. Tested for combustion gas and was positive for gas. Found a blown head gasket and sunk liners. It was pressurizing the cooling system and creating an air pocket and not letting coolant flow to the heater core. Getting a full overhaul now.