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How to Replace a Water Pump in a Johnson Outboard

by Will Charpentier

When your Johnson outboard has operated for 100 hours or when a year has passed since the last 100-hour mark, the Johnson maintenance schedule for your motor will remind you that it is time to replace the water pump. The water pump replacement kit you will need includes the grommets, O-rings, tubes, pieces and parts you'll need to complete the process.

Remove the four bolts that hold the pump housing in place with a 1/4-inch wrench. Push the cover and the insert to the top of the drive shaft. Pull the insert from the pump housing with needle nose pliers.

The top of the water pump housing contains a water tube grommet, a drive shaft O-ring and a drive shaft seal. Discard them and the insert as well; replacements are found in the water pump kit. Slide the impeller from the drive shaft, and discard it.

Remove the drive pin from its slot on the drive shaft. Remove the impeller plate. Clean any remaining gasket sealing compound from the impeller plate with a putty knife.

Apply a thin coat of gasket sealing compound to the outer diameter of the drive shaft seal, the O-ring, the outer side of the water tube grommet and the mating surfaces of the impeller plate, the lower unit and the pump housing. Insert the grommet into the large bore on the housing and the O-ring into the small bore.

Apply a thin coat of white marine grease to the outer diameter of the impeller and a thin coat of motor oil to the insert. Put a dab of white marine grease on the drive pin, return it to its slot and center the insert in the housing. Slide the impeller into place, turning it counterclockwise, to align it to the drive pin.

Return the pump housing and the insert to their place, sliding them down the drive shaft -- while turning the drive shaft clockwise -- to align them with the drive pin. Spread thread locker on the threads of the water pump bolts, thread them into their bores and use a torque wrench to tighten them to between 60 and 80 inch-pounds of torque.

Items you will need

  • Water pump replacement kit
  • 1/4-inch wrench
  • Needle nose pliers
  • Putty knife
  • Gasket sealing compound
  • White marine grease
  • Torque wrench

References

  • "Johnson Outboard Repair Manual -- 1973-1991"; 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.