Inboard Engine Overheating: Troubleshooting a New Malibu 5.7L

Question
I just purchased an 89 malibu with a 5.7L chevy in it. The motor is essentially new with 4 hours on it. The hours have been running in a garage with a hose attached to the water intake line. I personally saw it run for 20 minutes with no problems. Upon taking it out on the water for the first time, it overheated and died within 5 minutes... With as quick as it overheated, it obviously was getting no water to the engine... what could cause the different reaction?

Answer
Hi Jacob

Thank you for selecting the undersigned to reply to your question.

So long as there was no evidence of leaks anywhere, my first thought would be a damaged impeller. On the other hand, there could be a restriction or an obstruction of some sort. Did you pick up a piece of floating plastic that covered the fresh water intake? Did you check the belts for slippage? Is it possible the water pump failed? Did you check the thermostat?

Safe Boating
Ron