Neighbor asked me to install impeller because he sucked up some muck and noticed pee hole wasn't as strong. Fresh water outboard. I installed impeller(old one looked pretty good). I hooked up muffs and ran for a few minutes. The pee hole water started steaming and overtemp alarm came on. I cleared some debris from thermostat orifices and verified they opened and closed. Still overheating. I ran with thermostats and covers removed but no water makes it up to thermostat holes. Any help is greatly appreciated.