Sierra Marine Water Pump Kit 18-3150 Yamaha 20-25HP 2-Stroke Cooling System Rebuild

The Sierra 18-3150 Water Pump Kit is a complete internal rebuild kit designed for Yamaha 2-stroke 20HP and 25HP outboards. This kit restores proper cooling system performance by replacing all critical wear components inside the water pump assembly.

This is a without housing kit, meaning it includes the impeller, wear plate, cup, seals, and gaskets while reusing the existing pump housing. Ideal for routine maintenance or resolving weak water flow, overheating, or impeller failure.

Built to meet or exceed OEM specifications, Sierra components ensure reliable cooling performance and long service life in marine environments.

Key Features

• Complete internal water pump rebuild kit (housing not included)
• Includes impeller, wear plate, cup, gaskets, seals, and hardware
• Restores proper cooling water flow and engine temperature control
• Direct OEM replacement fit and performance
• Designed for Yamaha 2-stroke mid-range outboards
• Sierra limited lifetime warranty

Engine Compatibility

Yamaha Outboards (2-Stroke)

• 20 HP
• 25 HP

Fits 2-cylinder Yamaha 2-stroke engines with standard lower units.

Mariner (Yamaha-built models)

• 20 HP
• 25 HP

Cross-compatible with Yamaha-manufactured Mariner engines using the same platform.

Serial Number Fitment Notice

Fitment varies by model year and lower unit configuration.

Always confirm compatibility using your engine serial number, especially for:

• Early vs late production models
• Yamaha vs Yamaha-built Mariner variations

When This Part Needs Replacement

Replace the water pump kit if you notice:

• Weak or no telltale stream
• Engine overheating
• Reduced cooling at idle
• Impeller cracking, swelling, or hardening
• Engine sitting unused for extended periods

Recommended service interval: every 100 hours or annually

Installation Notes

• Housing is not included inspect and replace if worn
• Install impeller in correct rotation direction
• Apply marine grease during installation
• Replace seals and key components to prevent failure
• Ensure proper gasket sealing and torque to spec

Alternate / Superseded Part Numbers

OEM Cross References

• Yamaha:
  • 6L2-W0078-00-00
  • 6L2-W0078-A1-00

Aftermarket Cross References

• Mallory: 9-45606
• GLM: 12035

Shipping

Shipping: Ships same or next day for fast Canada wide shipping.

Parts Desk Insight

This kit is commonly confused with smaller 9.9/15HP kits they are NOT interchangeable.