How to Replace a Water Pump on a Tohatsu 3.5 Outboard

Updated July 20, 2017

The water pump in a Tohatsu 3.5 outboard motor pushes water from the lower unit of the motor to the top. When the pump is working properly, a small amount of water flows from the side of the lower unit, indicating that the pump is moving water through the motor and keeping it at a proper temperature. With the water comes mud, sand, rocks, shells and other debris that clogs and damages the pump. Without proper maintenance to remove this debris you will need to replace the water pump.

Remove the six bolts on the motor's lower unit with the wrench. The bolts are located just under the anti-cavitation plate and they connect the lower unit to the midsection.

Remove the bolt holding the trim tab to the bottom of the anti-cavitation plate. Set the trim tab and the bolt aside separately.

Detach the lower unit from the motor by removing the final bolt. Slide the lower unit out carefully and place it off to the side.

Pull the motor and shift shafts up carefully and slide them out of the motor. Set the shafts aside next to the tab.

Take the bolts off the water pump's plastic housing with the wrench. Lift the plastic housing off the pump. Remove the stainless steel cup and take the "O" ring out of the cup.

Remove the key way from the motor shaft by gently tapping it with a rubber mallet.

Slide the pump impeller out of the motor. Remove impeller gasket and the steel plate.

Open the new water pump kit and install the new water pump components in reverse order in which they were removed.

Grease the tops of the motor and shift shafts, the lower unit's housing, and the remaining bolts with an anti-seize compound.

Reinstall the motor and shift shafts, trim tap and lower unit into the motor.


When replacing the pump, change all of the pump components in order to get optimal usage and function from the new pump.

Things You'll Need

  • Work gloves
  • Adjustable wrench
  • Rubber mallet
  • Water pump kit
  • Anti-seize compound
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About the Author

Alisa Stevens has been writing articles and business/marketing materials since 1994. She has experience writing for and about a variety of industries, including the legal, transportation, government and education sectors. Stevens holds a B.A. in journalism and an M.B.A. from Arizona State University, as well as a J.D. from Loyola Law School.