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There are three reasons your outboard motor's impeller won't pump. The first is that the water stream fitting -- the outlet hole for an outboard motor's cooling system -- is clogged. Insects love to crawl up into it, but once there, they may become trapped and die. Once the cooling system is full of water, with no outlet, the impeller just agitates it, without cooling the motor. The second is that the water inlets are clogged; no water is getting to the pump, so it isn't pumping. Finally, the impeller may be damaged or worn beyond repair, requiring its replacement.
Items you will need
Thin piece of wire
Pump replacement kit
Locate the water stream fitting, found at the rear of the motor, at the bottom of the motor cover. Clear the fitting out out by poking a thin piece of wire into it and pulling any debris or insects out. Check the cooling water intakes and clean them out the same way, if they are clogged.
Connect a garden hose to your motor's flushing point or, if you don't have a single point flushing system, connect the hose to a device called a flushing attachment, and set the flushing attachment over the raw water intakes. Turn the water on, start your motor and warm it to its usual operating temperature. Look at the lower-rear part of your outboard's top cover while it is in operation.
Inspect the water stream fitting once more. If you see a stream of water pouring forth, the impeller is working. Shut the motor down immediately if you do not see a stream of water coming from the lower rear part of your motor's top cover; the problem lies with the impeller, not clogged intakes or a clogged water stream fitting.
Remove the nuts and bolts that connect the lower unit to the rest of the motor with a thin-wall socket. Pull the lower unit away from the motor carefully, lest you bend the driveshaft or shift shaft. The water pump is located on top of the lower unit.
Remove the bolts holding the water pump in place, using an adjustable wrench. Pull the pump cover up and over the top of the driveshaft. Grab the impeller and pull it off the driveshaft just as you did the pump cover.
Insert the new impeller -- from the pump replacement kit -- into the liner of the pump cover. Insert a new gasket in the groove on the underside of the water pump cover and apply a bead of gasket sealer to the gasket. Slide the pump cover and impeller back down the driveshaft and onto the pump's face plate on the lower unit. Bolt the pump cover back in place, tightening the bolts to 60 foot-pounds with a torque wrench.
- "Johnson Repair Manual -- 2.5 to 250 HP Models, 2002-2007"; Seloc Marine; 2007
Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.