How to Change a Water Pump on a Yamaha 15 Horse Power

Yamaha's 15-horsepower outboard motors use a water-cooled engine for propulsion. Cooling water drawn through a filter on the foot of the motor circulates through the engine water jacket by a low pressure, high volume, impeller-type water pump located in the foot of the motor. Driven by the motor shaft, the impeller is made of flexible rubber vanes. Age, heavy use and long periods of inactivity can cause the vanes to lose flexibility and crack, which causes pump failure and leads to insufficient cooling water delivered to the engine. Repair the motor by changing the water pump with a few common hand tools.

Things You'll Need

  • Ratchet
  • Socket set
  • New water pump impeller
  • New lower unit gasket
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Instructions

    • 1

      Remove the bolts holding the lower unit to the motor leg, using a ratchet and socket. Separate the lower unit slightly from the motor leg, until the shift shaft connection is exposed.

    • 2

      Remove the bolt connecting the upper and lower shift shaft, using a ratchet and socket. Remove the lower unit fully from the engine. Place the lower unit aside, in an upright position, and remove the old lower unit gasket.

    • 3

      Remove the bolts holding the water pump cover onto the motor leg, and remove the water pump cover. Observe the orientation of the old impeller. Pull the old impeller off its drive shaft.

    • 4

      Place the new impeller onto the drive shaft in the orientation observed in Step 3. Rotate it to collapse the vanes of the impeller while pushing it upwards into the pump housing.

    • 5

      Install the water pump cover and bolts. Tighten the water pump cover bolts securely with a ratchet and socket.

    • 6

      Install the new lower unit gasket onto the lower unit. Hold the lower unit in position under the motor leg and install the shift shaft connector bolt. Tighten the connector bolt securely with a ratchet and socket.

    • 7

      Push the lower unit fully into position on the motor leg. Position the lower unit gasket properly, and make certain it is not deformed. Install the lower unit bolts, and tighten them securely with a ratchet and socket.