Water Pump Impeller Kit – Fits Mercury/Tohatsu 4/5/6 HP 4-Stroke (Replaces 8M0120836, 3GR-87500-0)

Water Pump Impeller Kit – Fits Mercury/Tohatsu 4/5/6 HP 4-Stroke (Replaces 8M0120836, 3GR-87500-0)

This water pump impeller kit is designed for Mercury/Mariner and Tohatsu 4, 5, and 6 HP 4-stroke outboard engines. It serves as a crucial component for maintaining your engine's cooling system to prevent overheating.

This kit is a direct replacement for Mercury part number 8M0120836 and Tohatsu part number 3GR-87500-0.

• Installation: Direct replacement for a straightforward installation.
• Application: Essential for routine cooling system maintenance and repair.
• Compatibility: Fits specific Mercury and Tohatsu 4-stroke models.

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

Tohatsu

Technical Specifications

Package Contents

• 1 x Water Pump Impeller Kit (Replaces Mercury 8M0120836/Tohatsu 3GR-87500-0)

Note: The exact component breakdown of the kit is not fully documented in available sources. The primary component is the impeller.

Installation Guide

1. Safety First: Disconnect the engine's battery and remove the spark plug wire(s) to prevent accidental starting.
2. Access the Lower Unit: Disconnect any shift linkage and remove the bolts securing the lower unit (gearcase) to the midsection.
3. Remove Lower Unit: Carefully lower and separate the gearcase from the outboard's main housing.
4. Open Water Pump Housing: Locate the water pump assembly on top of the gearcase. Remove the bolts holding the housing cover.
5. Inspect and Remove Impeller: Note the rotational direction of the existing impeller fins. Remove the old impeller and the wear plate.
6. Clean and Install: Thoroughly clean the inside of the pump housing. Install the new impeller with a slight twisting motion in the correct rotational direction.
7. Reassemble: Reinstall the pump housing, ensuring all seals and gaskets are correctly seated. Torque bolts to manufacturer specifications.
8. Reattach Lower Unit: Guide the lower unit back into place, aligning the driveshaft and water tube. Reinstall mounting bolts and reconnect the shift linkage.
9. Test Operation: Reconnect the battery and test the engine using a water source (flushing muffs or in water) to confirm a strong water stream from the telltale outlet.

Troubleshooting & FAQ

How do I confirm this impeller fits my Mercury engine?

This kit is confirmed to fit Mercury 4, 5, and 6 HP 4-stroke EFI models with a serial number of 0R411838 or higher. It directly replaces OEM part number 8M0120836. Always verify your engine's serial number and original part number before ordering.

What are the signs of a failing water pump impeller?

The most common signs are engine overheating, an intermittent or weak water stream from the "telltale" indicator outlet, or finding brittle, cracked, or broken fins on the old impeller during inspection.

How often should I replace my water pump impeller?

For preventative maintenance, it is recommended to inspect the impeller annually and replace it every 1-2 years or every 100-200 hours of operation. Since this part is included in Mercury's 300-hour service kits, replacement at that interval is also a common practice.

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.