Water Pump Impeller Kit – Fits Johnson/Evinrude 40-75 HP (Replaces 391635, 18-3378)

Water Pump Impeller Kit – Fits Johnson/Evinrude 40-75 HP (Replaces 391635, 18-3378)

This water pump impeller kit provides a complete solution for Johnson/Evinrude 40-75 HP, 2-stroke outboard engines manufactured between 1979 and 1989. It is engineered to meet or exceed original equipment specifications for reliable cooling performance.

As a direct replacement, this kit corresponds to Johnson/Evinrude part numbers 391635, 439077, 390770, 396932, and 396933. It also replaces popular aftermarket kits, including Sierra 18-3378, 18-3380, 18-3385, and 18-3399; GLM 12210 and 12211; and Mallory 9-48204.

• Installation: Designed as a direct replacement for the original housing and components.
• Complete Assembly: Includes a 6-blade neoprene impeller, metal housing, wear plate, gaskets, seals, and stainless steel hardware.
• Fuel Compatibility: Suitable for gasoline-powered 2-stroke engines.

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 Johnson/Evinrude owners, here’s a guide to help you identify your engine’s serial/model: Johnson/Evinrude Serial Number Guide.

Technical Specifications

Package Contents

• 1 x Impeller (389589)
• 1 x Impeller Plate (320981)
• 1 x Housing (384087)
• 1 x Wear Plate Gasket (336530)
• 2 x Stainless Steel Bolt (909533)
• 2 x Stainless Steel Bolt (319126)
• 1 x Seal (315748)
• 1 x Water Tube Grommet (315837)
• 1 x O-Ring (303059)

Installation Guide

1. Before starting, disconnect the negative battery cable and shut off the fuel supply for safety.
2. Remove the lower unit (gearcase) from the outboard motor by unbolting it according to your service manual.
3. Locate and unbolt the existing water pump housing to access the old impeller and wear plate.
4. Clean all mating surfaces thoroughly, removing any old gasket material or debris.
5. Install the new wear plate gasket, wear plate, and impeller key onto the driveshaft.
6. Slide the new impeller onto the driveshaft, turning it clockwise to align with the key.
7. Lightly lubricate the interior of the new housing and the impeller with marine grease.
8. Install the new housing over the impeller, ensuring the bolts are tightened evenly to the manufacturer's specified torque.
9. Carefully reinstall the lower unit, making sure the water tube correctly aligns with the pump outlet.
10. Reconnect the battery, start the engine in a water-filled test tank or with a water flusher, and verify a steady stream of water from the tell-tale port.

Troubleshooting & FAQ

How do I confirm this kit fits my Johnson/Evinrude engine?
This kit is designed for most Johnson/Evinrude 40-75 HP 2-stroke outboards from 1979-1988. The most reliable method is to verify your engine's model and year against the "Compatible Engine Models" table. Additionally, cross-referencing your existing part numbers with those listed in the "Part Number Cross-Reference" section will ensure an exact match. The primary OEM part number this kit replaces is 391635.

What are the signs that my water pump impeller needs replacement?
Common symptoms of a failing impeller include the engine running hotter than normal or overheating, a weak or intermittent water stream from the tell-tale outlet, or a completely absent stream. Upon visual inspection, a worn impeller may appear cracked, brittle, or have deformed blades.

How often should I replace the water pump impeller?
For preventative maintenance, it is recommended to inspect the impeller annually. We suggest replacing the entire water pump kit every 1-2 years or every 100-200 hours of operation, whichever comes first. Replacement frequency should be increased if you operate primarily in saltwater or silty/sandy conditions.

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.