[Michael C Henry]

Are you shure the thermostat bypass is open.That short peice of hose between the manifold and coolant pump. Kinked ,layers seperated , even a blister inside the short hose pinching off any flow.
Then there is the head gaskets the coolant passage is blocked at one end ,usualy the front. Coolant goes in the front of the block ,is pushed rearward around the cylinders. up into the head at rear and then forward through the head then into the water channel in the intake manifold and to the thermostat. If the head gasket was on wrong coolant wouldn't circulate in the rear .Coolant would go in the front of the block and up to the head and out through the manifold, a short loop.Any coolant and air in the rear of the engine would stay in rear.