When i'm rising the stern and then lowering back in the water, the impeller is not getting enough water to pump it in the system and the engine is naturally overheating. I checked the impeller and is in order. When i've put it all the pieces of the pump back together, i did it under water and the pump being full of water, everything went fine, but as soon as i'm rising the stern, i've got the same problem. Please help me with this!