You need to check that there is no water leaking out around the top engine mounts, It might be that the Water pickup tube is not sitting in the bottom of the powerhead. Also make sure the sealing tube between the water pump and the bottom of the pick up tube is ok.
Can give you the part numbers as i dont know how old the engine is, Whats the serial number and i can tell you what the part numbers are.
Have you checked the Thermostat is ok, Or it could just be the tell tale hose (from the powerhead to the outlet) is blocked. This is quite common.