OK...I bought a boat. It has a 1998 Johnson 9.9 on it. It hadn't run for a while, so I had the impeller replaced. I took it out for the first trip Tuesday. After running for about 30 min, I stopped and put it in neutral so we could get ready to troll. While we were gearing up, my hot light and alarm went off...motor wasn't pumping water. We let it cool down, blew the water-out tube out, and tried it again. It pumped fine for a few minutes, but then began to sputter, and the alarm/light came on again. Shut it down and brought it home. We took it apart and the impeller is fine, what else might cause the motor to overheat, and the water to quit being pumped through?