Water Pump Impeller Kit – Fits Yamaha 25-40 HP 4-Stroke (Replaces 66T-W0078-00-00)

Water Pump Impeller Kit – Fits Yamaha 25-40 HP 4-Stroke (Replaces 66T-W0078-00-00)

This aftermarket water pump impeller kit is designed for select Yamaha 4-stroke outboard motors, including 25 HP (T25), 30 HP (F30), and 40 HP (F40) models. It also fits specific 40 HP 2-stroke models manufactured from 1998 onwards. Please consult the compatibility table to confirm fitment for your specific engine model and year.

This assembly is a direct replacement for OEM part numbers and includes the housing, impeller, wear plate, and all necessary gaskets, seals, and hardware for a complete overhaul of the water pump unit.

• Engineered as a direct-fit replacement for a straightforward installation.
• The 6-blade impeller is made from durable neoprene rubber for reliable performance.
• Includes a new marine-grade metal housing and all required installation hardware.

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 (6H4-44352-02-00/6H4-44352-00-00)
• 1 x Pump Housing Cover (63D-44312-00-00)
• 1 x Cartridge Insert (63D-44322-00-00)
• 1 x Cartridge Outer Plate (66T-44323-00-00)
• 1 x Water Pump Gasket (63D-44316-00-00)
• 1 x Water Seal Damper (663-44366-00-00)
• 1 x O-Ring (93210-59MG7-00)
• 1 x Woodruff Key (90280-03M03-00)
• 4 x Bolts with Washer (90119-08M15-00)

Installation Guide

1. Disconnect the Battery: Ensure the engine is off and disconnect the battery's negative terminal for safety.
2. Access the Lower Unit: Position the engine securely and locate the lower unit (gearcase). You may need to tilt the engine up.
3. Drain Gear Lube: Place a drain pan under the lower unit and remove the upper and lower gear lube drain screws to empty the oil.
4. Remove Lower Unit: Loosen and remove the bolts securing the lower unit to the engine's midsection. Keep track of bolt lengths and positions.
5. Detach Lower Unit: Carefully separate the lower unit from the driveshaft housing. The driveshaft and shift shaft will disengage.
6. Access Water Pump: With the lower unit removed, locate the water pump housing on top of the gearcase.
7. Disassemble Pump: Remove the four bolts holding the water pump housing cover. Lift off the housing to expose the impeller.
8. Remove Old Components: Slide the old impeller off the driveshaft. Remove the Woodruff key, wear plate, and old gaskets.
9. Clean and Prepare: Thoroughly clean all mating surfaces, removing any old gasket material or corrosion.
10. Install New Kit: Install the new gasket, outer plate, cartridge insert, and Woodruff key. Lightly grease the new impeller and slide it onto the driveshaft while turning clockwise to seat the blades.
11. Reassemble and Reinstall: Place the new housing over the impeller, ensuring seals are seated correctly. Reinstall and tighten the bolts. Carefully guide the lower unit back into place, aligning the shafts and water tube. Reinstall lower unit bolts.
12. Final Steps: Refill the gearcase with fresh marine gear lube, reinstall the drain screws, and reconnect the battery. Test the engine on a water supply to verify a strong water stream from the tell-tale.

Troubleshooting & FAQ

Q: How do I confirm this kit fits my Yamaha engine?

A: The best way is to match your engine's model name, horsepower, and year of manufacture to the detailed list in our "Compatible Engine Models" table. For Yamaha owners, the linked serial number guide can help you precisely identify your model if you are unsure.

Q: What are the signs that my water pump impeller is failing?

A: Common symptoms include the engine overheating, especially at idle or low speeds, and a weak or non-existent water stream from the "tell-tale" outlet. Upon inspection, a failing impeller may appear brittle, have cracked or missing blades, or be permanently deformed.

Q: How often should I replace the water pump impeller?

A: For preventative maintenance, it is recommended to replace the impeller every 1 to 2 years or every 100-200 hours of operation. Replacement frequency should be increased if the engine is used in saltwater or sandy/murky conditions.

Q: The title says 4-stroke, but the chart lists some 2-stroke models. Does it fit both?

A: Yes, while this kit primarily fits the listed 25-40 HP 4-stroke Yamaha models, it is also designed to be compatible with select 40 HP 2-stroke models from 1998 onwards, such as the 40X, 40XWT, and E40X. Always verify your specific model in the compatibility table.

Q: OEM vs. Aftermarket?

A: 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.

Q: How fast do you ship and how much does it cost?

A: 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.

Q: What is your warranty and return policy?

A: 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.