waMariner 1985 50hp 4cyl over heat problem

When the boat is idling water comes out the exit just like it should. But when I get on plain the motor gets hot and very little water and steam comes out hte exit. We put a new water pump kit on prior to this happening. Any ideas?
Thank you

Leak in the water tube, or an old impeller blade that broke off and is plugging up the water passages.

Jeff

Did you have this problem before you did the water pump? Sometimes if you get all the impeller blades but one turned the right way they can act like this too. Definitely a water tube could be leaking but I'm thinking along the lines of more pump action = less water. You should rotate the drive shaft clockwise as you lower the waterpump housing onto the impeller making sure that each blade is bent in the same direction. I hope that's the problem because if it's not I'll bet you a one eyed watch dog you have an exhaust leak in the exhaust plate caused by corrosion pitting all the way through the plate or a blown exhaust gasket. The exhaust plates can be hard to find but, if it's just a gasket it's an easy fix. A leak like that would push exhaust into the cooling tract as engine speed went up, raising the pressure in the cooling system and keeping the water at bay. When it quits peeing do you get steam or smoke? That plate on side of the engine with a dozen bolts in it is where your problem may lie. If you see signs of leaking or loose bolts there then it's worth looking into.