Water Pump Impeller Repair Kit – Fits Mercury/Tohatsu 9.9-20 HP 4-Stroke EFI (Replaces 8M0137849, 8M0135821)

Water Pump Impeller Repair Kit – Fits Mercury/Tohatsu 9.9-20 HP 4-Stroke EFI

This water pump impeller repair kit is designed for Mercury Marine/Mariner 9.9, 10, 15, and 20 HP 4-Stroke EFI outboard engines (2020 and newer) with serial numbers 0R833820 and up. It also fits compatible Tohatsu/Nissan 15-20 HP (MFS) 4-Stroke outboards.

This kit serves as a direct replacement for Mercury part numbers 8M0137849, 8M0135821, 98-8M0135821, 8M0134484, 46-8M0122064, and Tohatsu part number 3RS-87322-1. It provides all necessary components for a complete water pump service to restore your engine's cooling performance.

• Engineered for direct-fit installation, replacing OEM components without modification.
• Features a durable marine-grade nylon water pump housing with a stainless steel (SS316) wear plate and liner.
• Includes a high-performance CR-Neoprene water pump impeller and seals for longevity.

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 Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Confirm your engine model/year in the table below.

Mercury/Mariner

Nissan/Tohatsu

Technical Specifications

Package Contents

• 1 x Water Pump Impeller (334-65021 / 3LD-65021)
• 1 x Housing
• 1 x Insert Cup
• 1 x Wear Plate
• 2 x Gaskets
• 1 x Key
• 1 x Seal Kit

Installation Guide

1. Disconnect Power: Disconnect the battery and spark plug wires for safety.
2. Drain Gearcase: Drain the gearcase lubricant from the lower unit.
3. Remove Lower Unit: Unbolt and carefully detach the lower unit (gearcase) from the outboard's upper casing. You may need to disconnect the shift linkage.
4. Access Water Pump: With the lower unit removed, locate and unbolt the water pump housing.
5. Remove Old Components: Take note of the order of components. Remove the old housing, impeller, wear plate, gaskets, and seals. Clean all mating surfaces thoroughly.
6. Install New Impeller: Lightly lubricate the new impeller with silicone grease or soapy water. Install the new key on the driveshaft and slide the new impeller on, turning the driveshaft clockwise to bend the vanes correctly.
7. Reassemble Kit: Install the new gaskets, wear plate, insert cup, and housing. Ensure all components are seated correctly.
8. Reattach Lower Unit: Reinstall the lower unit, ensuring the driveshaft, water tube, and shift shaft align correctly. Torque bolts to manufacturer specifications.
9. Refill and Test: Refill the gearcase with fresh lubricant. Reconnect the battery and start the engine in a test tank or with a water flusher to confirm water is exiting the tell-tale port.

Troubleshooting & FAQ

How do I confirm this fits my Mercury EFI engine?

This kit is specifically for 9.9-20 HP EFI 4-stroke models from 2020 and newer. The most important checkpoint is your engine's serial number. It must be 0R833820 or higher for this kit to be compatible.

What are the signs of a failing water pump?

Common signs include a weak or non-existent water stream from the "tell-tale" outlet, engine overheating alarms, and reduced engine performance. A dry, cracked, or brittle impeller found during inspection also indicates a need for replacement.

How often should the water pump impeller be replaced?

As a preventative maintenance measure, it's recommended to inspect the impeller annually and replace it every 1-2 years, or after every 100-200 hours of use, depending on operating conditions (e.g., saltwater vs. freshwater).

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.