An outboard motor's water pump pulls water into the engine compartment with a rubber impeller to cool down the motor. Whenever the motor runs, the water pump must also run to prevent overheating. Over time, the impeller may break down and other moving parts inside the water pump may fail due to the constant motion. Instead of replacing the entire outboard motor, you can remove the defective water pump and install a replacement.
Take out the bolts that connect the motor to the engine compartment. Pull the bottom portion of the motor out of the top portion. Disconnect the wiring harness that connects the two sections of the motor.
Set the lower portion of the motor into an engine vise and tighten the clamp. Remove the bolts that hold the water pump onto the engine housing. Consult your outboard motor's owner's manual for the location of the water pump on your specific make and model. Remove the pump housing so you can access the impeller.
Lift off the impeller and driveshaft sprocket. Remove and discard the gaskets from the old water pump. Use a stiff wire brush to scrub any debris off the surface underneath the gaskets.
Apply a thin covering of engine oil to the new gaskets. Place the gaskets, sprocket and replacement impeller onto the driveshaft. Replace the water pump housing, turning the driveshaft as you press down on the housing. You should feel the housing snap into place when the driveshaft is aligned properly. Replace the lower engine housing and tighten the bolts.
Remove the lower portion of the motor from the vise and slide it back into the upper housing. Tighten the bolts that connect the two halves of the motor and attach the wiring harness. Place the motor back into the engine compartment and tighten the bolts. Test the motor to make sure the new water pump works correctly before taking your boat out on the water.
- Jupiterimages/Photos.com/Getty Images