Water Pump Impeller Service Kit – Fits Yamaha 2-Stroke 40/50 HP (Replaces 6H4-W0078-00)

Water Pump Impeller Service Kit – Fits Yamaha 2-Stroke 40/50 HP (Replaces 6H4-W0078-00)

This water pump impeller service kit is designed for Yamaha 2-Stroke 40 HP (1995–2005) and 50 HP (1998–2009) outboard motors. It provides a reliable, direct-replacement solution for maintaining your engine’s cooling system.

This kit is a direct replacement for Yamaha part numbers 6H4-W0078-00, 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00, and Sierra part numbers 18-3408 / 18-3429.

• Engine placement: Lower Unit.
• The impeller is constructed from high-quality, durable Neoprene for optimal performance and longevity.
• Engineered to meet or exceed original equipment manufacturer (OEM) specifications for a precise fit and function.

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 Water Pump Impeller (6H4-44352-00)
• 1 x Wear Plate
• 1 x Insert Cup
• 1 x Water Pump Gasket
• 1 x Key
• 1 x Water Seal
• 1 x "O"-Ring

Installation Guide

1. Disconnect the battery and remove the propeller.
2. Drain the gearcase oil from the lower unit.
3. Unbolt and carefully lower the gearcase from the outboard's driveshaft housing.
4. Remove the bolts securing the water pump housing cover.
5. Take note of the old impeller's rotational orientation before removing it.
6. Remove the old impeller, plate, cup, gaskets, and seals from the housing.
7. Clean all mounting surfaces thoroughly, removing any old gasket material or debris.
8. Install the new wear plate, gasket, and insert cup into the housing.
9. Slide the new key and impeller onto the driveshaft. Apply a light coat of marine grease to the housing interior and ensure impeller vanes point in the correct rotational direction.
10. Reinstall the water pump housing and tighten bolts to the manufacturer's specified torque.
11. Reattach the lower unit to the driveshaft housing and refill the gearcase with new oil.
12. Reinstall the propeller and test the engine using a water supply (flushing muffs) to verify correct water pump operation.

Troubleshooting & FAQ

How do I confirm this kit fits my engine?

This kit fits specific Yamaha 2-Stroke 40 HP and 50 HP models from 1995-2009. Please check the Compatible Engine Models table on this page and verify your engine's model and year range. Cross-referencing your existing part number with our list also ensures a correct match.

How often should I replace the water pump impeller?

For preventative maintenance, it is recommended to replace your water pump impeller every 1-2 years or every 100-200 hours of use, depending on operating conditions. Frequent use in saltwater or sandy/silty water may require more frequent inspections.

What are the signs of a failing water pump?

Common signs include the engine overheating at idle or low speeds, a weak or intermittent water stream from the "telltale" outlet, and visible cracks or damage on the old impeller upon inspection.

OEM vs. Aftermarket?

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.