Re: Nissan 5hp impeller
A parts catalog will definitely help you here. See Tohatsu Guru's
http://www.internetoutboards.com/PartsCatalogMenu.htm
The water pump is attached to the top of the LU with 4 bolts. You need to drop the LU (2 bolts) and then you can service the impeller. Don't lose the pin that indexes the impeller to the shaft.
I have repaired a lot of these reliable old beaters. Usual problems are fuel-related. A common issue is the rubber washer for the vent at the fuel tank cap (if not remote-tank-equipped.) If stuck shut, a vacuum slowly develops in the tank, slowing -- and eventually stopping fuel flow to the carb. On remote tank units, there is sometimes a leak that allows air into the fuel line, causing similar symptoms.
Yes, if it overheats enough, it will start to seize -- slow down, and eventually stop, just like any other severely-overheated motor. Has to get bloody hot for that to happen. Often gets hot enough to discolor the paint on the cylinder. Most of these will re-start after cooling down, though we did recently have one that warped so badly (due to overheating) that it was scrap. Check the cooling telltale "pee hole", located at the underside aft area of the powerhead. Should flow freely all the time, indicating that the cooling system is pressurized. The telltale can get plugged with debris. You can clear a plugged telltale with a stiff wire.
Obviously, never run the motor out of the water -- not even for a second. It's not even good to crank the motor by pulling the recoil starter when the water pump is dry.
HTH
