I had an unusual water pump experience on my 2001 Nautique. Upon testing at the beginning of the season, the impeller would not properly draw water from a bucket full of water. Headers would begin to overheat. I removed the impeller and it appeared fine, reinstalled pump....same issue. Complete rebuild kit installed, new impeller new o ring, new brass plate, everything works like it should. Perhaps a test to consider.... remove the raw water intake hose by the transmission, stick a garden hose into the intake hose and run the boat..... if your headers are cool and temps ok, I doubt there is a blockage. Next, stick the raw water intake hose into a bucket that you are filling with a garden hose.... run the motor, you should feel strong suction at the intake hose end, headers should remain cool.... if not, and all of your hose connections are tight, try a full pump rebuild kit. Good luck, there is an answer.