How to Change the Water Pump on a 25 HP Yamaha Outboard Motor

Written by mike frees
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The water pump in your Yamaha outboard operates continuously to keep cool water flowing through your engine, preventing overheating and serious damage. The resulting wear means that, under normal operation, your water pump should be rebuilt or replaced once per year. Replacing the water pump is not a difficult job for the handy home mechanic with basic hand tools.

Skill level:
Moderate

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Things you need

  • Replacement Yamaha water pump
  • Hand tools: Socket wrenches, box wrenches, screwdrivers
  • Emery cloth
  • Marine grease

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Instructions

  1. 1

    Disconnect the spark plug wires. If the engine has electric starting, disconnect the battery cables as well. Place the engine in reverse. Loosen the bolts connecting the upper and lower shift linkage rods and disconnect them.

  2. 2

    Support the lower unit and remove the bolts connecting it to the engine (there are four bolts on the 2-cylinder engine, five on the 3-cylinder model.) Pull the lower unit straight down and out. Secure it in an upright position to work on the water pump. Clean the driveshaft with emery cloth and lightly coat it with grease to ease the removal of the water pump components.

  3. 3

    Remove the four screws holding down the water pump body. Carefully pry up the pump body, using two screwdrivers to evenly free it on both sides. Lift the pump body off of the driveshaft. Pry up the water pump impeller and remove it. Remove the metal drive key from its slot in the driveshaft. Remove the water pump wear plate and clean off any old gasket material or corrosion with emery cloth.

  4. 4

    Slide the new wear plate down over the driveshaft and align it with the screw holes. Lightly grease the drive key and replace it in the driveshaft slot. Slide the new impeller down over the driveshaft, aligning it on the drive key. The Yamaha water pump uses a rubber O-ring around the edge of the water pump body; lightly grease the O-ring and push it into place in the groove. Slide the water pump body down the driveshaft and over the impeller. While pressing down lightly, turn the driveshaft clockwise until the pump body fits into place. Reinstall the four screws on the pump body. Push the water tube grommet into the pump housing.

  5. 5

    Carefully lift the lower unit back into the engine, aligning the driveshaft with its housing. Reinstall the bolts to secure the lower unit in place. Reconnect the shift linkage to complete the job. Be sure to run the engine and confirm that a stream of water is exiting the telltale to verify that the water pump is working correctly.

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