Water Pump Impeller Kit for Yamaha 25HP-40HP Outboards

Water Pump Impeller Kit – Fits Yamaha 25HP-40HP Outboards (Replaces 66T-W0078-A0)

This water pump impeller service kit is designed for Yamaha 2-stroke and 4-stroke outboard engines ranging from 25HP to 40HP, covering models from approximately 1993 to 2006. It provides the essential components needed to restore the performance of your engine's cooling system.

This kit is a direct replacement for Yamaha OEM part numbers, including 66T-W0078-A0, 66T-W0078-A0-00, 66T-W0078-00-00, and 66T-W0078-01-00. It also cross-references with Sierra 18-3432 and GLM 89890.

• Engineered as a direct-fit replacement for straightforward installation.
• Restores cooling efficiency to prevent engine overheating.
• Includes all essential components for a standard water pump service.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Yamaha owners, here’s a guide to help you identify your engine’s serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Impeller
• 1 x Water Pump Housing Gasket
• 1 x Wear Plate to Gear Case Mounting Gasket
• 1 x Wear Plate to Pump Housing Gasket
• 1 x Impeller Key
• Additional gaskets and O-rings may be included depending on specific kit configuration.

Installation Guide

1. Safety First: Disconnect the battery and remove the propeller before starting.
2. Access the Lower Unit: Drain the gearcase oil. Then, unbolt and carefully remove the lower unit (gearcase) from the outboard motor.
3. Remove Pump Housing: Locate the water pump assembly on top of the gearcase. Remove the bolts securing the water pump housing.
4. Inspect and Replace Impeller: Lift off the housing and slide the old impeller off the driveshaft. Note the direction of the old impeller's vanes.
5. Replace Components: Clean all surfaces. Install the new gaskets, wear plate, and impeller key. Slide the new impeller onto the shaft, rotating it in the correct direction to seat the vanes.
6. Reassemble: Reinstall the pump housing, ensuring a proper seal. Reattach the lower unit to the engine, refill the gearcase oil, and reconnect the battery.
7. Test Operation: Start the engine in water and verify a strong, steady stream of water from the tell-tale outlet.

Troubleshooting & FAQ

How do I confirm this kit fits my engine?
First, check your engine's model, horsepower, and year against our compatibility table. Second, verify that your existing part number matches one of the OEM or aftermarket numbers listed in the cross-reference section. This ensures the most accurate fit.

What are the signs of a failing water pump impeller?
Common symptoms include an engine that is overheating, a weak or intermittent water stream from the tell-tale (water indicator), or visible damage like cracked or missing vanes on the old impeller upon inspection.

How often should I replace the water pump impeller?
For preventative maintenance, we recommend inspecting the impeller annually and replacing it every 1 to 2 years (or 100-200 hours). Replacement frequency may depend on usage, water conditions (saltwater vs. freshwater), and storage.

Is this an OEM part?
This listing is an aftermarket replacement part, not an OEM component. We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.