How to Replace an Outboard Water Pump Impeller: A Step-by-Step Guide

The water pump impeller is a crucial component of your outboard’s cooling system. Over time, it wears out and can lead to overheating and serious engine damage. Replacing it regularly is essential for reliable performance. Follow this guide to replace your impeller step by step.

Tools and Materials You’ll Need

  • Replacement impeller kit (check your manual for the correct part)
  • Wrenches or socket set
  • Screwdrivers
  • Marine grease
  • Clean rags or paper towels
  • Container to catch water or oil
  • Service manual (optional but recommended)

Important Safety Tips

  • Ensure the engine is off and in neutral gear before starting.
  • Work on a stable surface and support the engine if necessary.
  • Keep small parts organized as you remove them.

Step-by-Step Impeller Replacement

1. Remove the Lower Unit

Disconnect the battery. Place the engine in neutral. Remove the bolts holding the lower unit to the midsection. Carefully slide the lower unit down and off the driveshaft.

Removing lower unit to access water pump

2. Remove the Water Pump Housing

Locate the water pump housing on the top of the lower unit around the driveshaft. Remove the bolts securing the housing and lift it off. Take note of the impeller orientation and the placement of gaskets and seals.

Removing lower unit to access water pump

3. Install the New Impeller

  • Clean the inside of the housing and the plate below it.
  • Apply a thin layer of marine grease to the plate and inside walls of the housing.
  • Insert the new impeller, making sure the blades are bent in the correct direction of rotation.
  • Reinstall the housing and torque the bolts to specification.
Removing lower unit to access water pump

4. Reinstall the Lower Unit

Carefully slide the lower unit back into place, making sure the driveshaft and shift shaft align properly. Tighten all bolts securely and reconnect the battery.

Test the Cooling System

Start the engine and check for a strong, steady stream of water coming from the telltale ( pee hole ). This indicates the pump is working properly. If not, double-check your installation.

Pro Tip: For torque specifications, diagrams, and detailed instructions specific to your engine model, refer to your service manual.

Conclusion

Replacing the water pump impeller is an important maintenance task that ensures your engine stays cool and protected. Following this guide step by step will help keep your outboard running smoothly and avoid costly repairs.

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