How to Change an Impeller in a 9.9 HP Johnson Outboard

by Will Charpentier

Changing the impeller on the Johnson 9.9-horsepower outboard is a straightforward affair that ensures your motor's cooling system will remain healthy. The impeller is the heart of the cooling system, moving the water from the cooling water inlets, throughout the cooling galleries of the motor's powerhead where the heat from the motor's operation is transferred to the water. The water is then discharged through the water stream fitting at the back of the motor. Inspect and change the impeller according to Johnson's outboard maintenance schedule, and your motor will stay cool for years.

Take out the bolts -- there are either three or four, depending on the model year -- that hold the water pump in place on the lower unit, using a 1/4-inch socket. Work the cover up and off the top of the driveshaft. Extract the impeller from the housing using a pair of needle-nose pliers.

Remove the impeller drive pin from the driveshaft. Pull the the water tube grommet, located on the top of the pump cover, out of its bore and discard it. Pull the pump insert out of the water pump cover with the needle nose pliers.

Apply gasket sealant to the outer diameter of the replacement driveshaft seal. Install the new seal, from the pump replacement kit, into the top of the pump housing, so that the rounded edges of the seal face toward the impeller.

Apply gasket sealant to the impeller housing O-ring and to the outside of the water tube grommet. Push the O-ring into the larger of the two bores on top of the pump housing. Push the grommet into to the smaller round boss on top of the housing. Push the new impeller into the the insert and push the insert into the pump housing. Wet the end of the drive pin with petroleum jelly and insert it into its place on the driveshaft.

Turn the driveshaft to the right -- clockwise when viewed from above -- to prevent damage to the impeller vanes. Apply a light coating of thread locking compound to the water pump mounting bolt threads and install them, tightened as much as possible by hand, then use a torque wrench to tighten them to between 60 inch-pounds and 84 inch-pounds.

Items you will need

  • 1/4-inch socket
  • Needle nose pliers
  • Pump replacement kit
  • Gasket sealant
  • White marine grease
  • Torque wrench

References

  • "Johnson Repair Manual 2.5 to 250 HP Models, 2002-2007"; Seloc Marine; 2007

About the Author

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.