Water Pump Impeller Kit – Fits Johnson/Evinrude 40-50 HP (Replaces 438597)

Water Pump Impeller Kit – Fits Johnson/Evinrude 40-50 HP (Replaces 438597)

This water pump impeller service kit is designed for Johnson/Evinrude 2-Stroke outboard motors, specifically 40, 45, 48, and 50 HP models manufactured between 1989 and 1998. It serves as a complete replacement solution to maintain your engine's cooling system for optimal performance and reliability.

It directly replaces multiple part numbers, ensuring wide compatibility for the specified engine range. Please note this kit is for models using the small housing variant.

• Includes all necessary components for a standard rebuild: impeller, housing, wear plate, gasket, and seals.
• Engineered for a direct OEM fit, simplifying the installation process.
• Features a durable 3-vane impeller design for efficient water circulation.

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 (18-3104-1)
• 1 x Housing
• 1 x O-Ring
• 1 x Gasket
• 1 x Wear Plate
• 1 x Insert Cartridge
• 1 x Water Seal/Grommet

Installation Guide

1. Disconnect the negative battery cable for safety.
2. Remove the lower unit (gearcase) from the outboard's driveshaft housing.
3. Unscrew the bolts securing the water pump housing and remove the housing.
4. Carefully slide the old impeller off the driveshaft, and remove the impeller key.
5. Remove the old gasket and wear plate, ensuring the mounting surface is clean and free of debris.
6. Install the new wear plate and gasket onto the lower unit.
7. Place the new impeller key in the driveshaft slot and slide the new impeller on, turning the shaft clockwise to bed the vanes.
8. Install the new O-ring in the housing and place the housing over the impeller.
9. Secure the housing with the mounting bolts, tightening them to the manufacturer's specified torque.
10. Re-install the lower unit onto the outboard motor.
11. Reconnect the battery and test the engine in water, confirming a steady water stream from the tell-tale outlet.

Troubleshooting & FAQ

How do I confirm this fits my engine?

A: Review the "Compatible Engine Models" table to verify your engine's model, horsepower, and year range. It is crucial to confirm your engine uses the small housing design and that your original part number matches one of the numbers listed in our cross-reference section.

What are common signs of a failing water pump impeller?

A: Key indicators include the engine overheating, a weak or inconsistent water stream from the tell-tale port, or discovering the impeller has cracked, brittle, or worn vanes during a visual inspection.

How often should I replace the water pump impeller?

A: As a preventative maintenance measure, it is recommended to replace the impeller every 1 to 2 years or after every 100-200 hours of operation. Frequency should be increased if operating in saltwater or sandy/silty 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.