No coolant flow through heater core
 

My 94 318is has a new water pump with a metal impeller, and new thermostat and I don,t seem to have enough pressure to push the coolant through the heater cores. My heater control valve plungers were stuck so I removed them to allow coolant to flow straight through. I can disconnect the inlet hose to the heater cores and coolant will flow freely with the engine running but as soon as I lift it up to the angle it is connected in the flow stops completely. Any advice on this would be greatly appreciated as this has had me perplexed for quite some time now and winter is coming on.

Did you compare it to the old impeller. It almost sounds like the impeller blades are at the wrong angle. Could also be a thermostat that is not opening all the way.

Bad pump or bad thermostat

You wont get flow through the radiator until the engine is hot and the thermostat opens. Is the engine hot when you have the top hose disconnected to check flow?

Make sure the pump impeller is mated tightly to the pump shaft .