I am looking at buying a little boat witha 50 horse merc from a guy at church. Boat has sat covered for a couple years in his garage. Took it out to the lake to test it the other day and went about 1/2 mile before the overheating alarm went off. Looked back and there was no pee stream. used the trolling motor to get back to the ramp. Took it to a friend and he changed the impeller but still no water coming out. Is there a chance its just a mud dobber nest? how would you flush that out? any chance its a more serious problem? thanks.