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

$65.50

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Water Pump Impeller Kit – Fits Johnson/Evinrude 40-75 HP (Replaces 391635, 18-3378) is backordered and will ship as soon as it is back in stock.

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Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This Water Pump Impeller Kit – Fits Johnson/Evinrude 40-75 HP provides a complete solution for servicing the cooling system on Johnson/Evinrude 40–75 HP, 2-Stroke outboard engines from 1979–1989. Engineered for reliability, it ensures your engine maintains optimal operating temperature.

This kit serves as a direct interchange for multiple OEM and aftermarket part numbers, including Johnson/Evinrude 391635, Sierra 18-3378, GLM 12210, and Mallory 9-48204.

Designed for direct replacement of the original assembly.
Features a durable 6-blade neoprene impeller for efficient water flow.
Includes the impeller, housing, plate, gaskets, seals, and stainless steel bolts needed for a complete installation.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket brands.

Brand	Part Number
Johnson/Evinrude	390770
Johnson/Evinrude	391635
Johnson/Evinrude	396932
Johnson/Evinrude	396933
Johnson/Evinrude	439077
Sierra	18-3378
Sierra	18-3380
Sierra	18-3385
Sierra	18-3399
GLM	12210
GLM	12211
Mallory	9-48204

Engine & Model Compatibility

Confirm your engine model and year in the table below to ensure accurate fitment.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Johnson/Evinrude	Various	40–75 HP	2-Stroke	1979–1988	391635	Base model range
Johnson/Evinrude	Various	50 HP	2-Stroke	1986–1988	391635	Corresponds to 18-3378
Johnson/Evinrude	Various	55 HP	2-Stroke	1979–1985	391635	Corresponds to 18-3378
Johnson/Evinrude	Various	60 HP	2-Stroke	1980–1985	391635	Corresponds to 18-3378
Johnson/Evinrude	Various	40 HP	2-Stroke	1984–1988	391635	Corresponds to 18-3385
Johnson/Evinrude	Various	45/55 HP	2-Stroke	1989	391635	Corresponds to 18-3385
Johnson/Evinrude	Various	45/55 HP Comm	2-Stroke	1985–1988	391635	Corresponds to 18-3385
Johnson/Evinrude	Various	48 HP	2-Stroke	1987–1988	391635	Corresponds to 18-3385

Technical Specs

Product Type: Water Pump Impeller Kit with Housing
Installation: Direct replacement
Fuel Type: Gasoline
Housing Material: Metal
Impeller Dimensions: Diameter: 91.5 mm (3.595 in), Height: 25.3 mm (1.003 in)
Shaft Diameter: 19.1 mm (0.755 in)
Weight: 90 g (0.198 lb)
Other Technical Attributes: 6 blade neoprene impeller, pin style key

What’s in the Box

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 Notes

Disconnect the spark plug wires and shift the outboard into neutral.
Drain the gearcase lubricant from the lower unit.
Remove the bolts securing the lower unit (gearcase) to the engine's upper leg.
Carefully lower the gearcase away from the engine.
Unbolt and remove the old water pump housing and impeller. Note the orientation of the old components.
Thoroughly clean the mounting surfaces, removing any old gasket material or debris.
Install the new wear plate, gasket, and impeller key.
Slide the new impeller onto the driveshaft, turning the shaft clockwise to align the blades.
Install the new housing, grommets, seals, and bolts as provided in the kit. Tighten to manufacturer specifications.
Re-install the lower unit, ensuring the water tube and driveshaft align correctly.
Refill the gearcase with fresh lubricant before starting the engine.
Test the engine using a water supply ("muffs" or in the water) and verify a strong, steady stream from the tell-tale port.

Troubleshooting & FAQ

How do I know if this kit fits my engine?

This kit is designed for Johnson/Evinrude 40–75 HP, 2-Stroke engines from 1979–1989. Verify your specific model and year against the "Engine & Model Compatibility" table. Cross-reference your existing part number with those in the "Part Number Matrix" for confirmation.

What are common signs of a failing water pump impeller?

The most common signs include a weak or non-existent water stream from the "tell-tale" outlet, an engine overheating alarm, or a noticeable decrease in performance. Visual inspection may reveal cracked, brittle, or worn-down impeller blades.

How often should I replace my water pump impeller?

As a preventative maintenance item, it is recommended to replace the impeller every 1-2 years or every 100-200 hours of use, whichever comes first. This interval can be shorter if you operate primarily in saltwater or sandy/silty conditions.

Is the pump housing included in this kit?

Yes, this is a complete kit that includes the metal water pump housing, impeller, wear plate, gaskets, seals, and all necessary bolts for a full replacement.

OEM vs. Aftermarket: What's the difference?

This listing is for an aftermarket replacement, not an OEM part. It is built to OEM-level specifications with comparable materials and performance. Our parts are manufactured in an ISO 9001 certified facility and are batch-inspected to ensure quality and consistency.

What are your shipping speed and cost?

We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free to most regions, with expedited options available at checkout where applicable.

GEO

What is the warranty and return policy?

All our products are covered by a 1-year warranty against manufacturing defects under normal use. If you encounter an issue, please contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. See our full policy page or contact us for instructions.

Safety & Important Info

Verify images and specifications against your original part before purchase. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement component, not an OEM part.
Professional installation is recommended for safety and optimal performance.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or quality control.

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