Water Pump Impeller Kit – Fits Mercury/Mariner 8-9.9 HP 4-Stroke 209cc

Water Pump Impeller Kit – Fits Mercury/Mariner 8-9.9 HP 4-Stroke 209cc (Replaces 8M0120837, 3V1-87500-0)

This comprehensive maintenance kit includes all the necessary components to service the water pump and cooling system on select Mercury, Mariner, and Tohatsu 8-9.9 HP 4-Stroke (209cc) outboards. It is designed for models from 2018 and newer (serial number 0R042475 and above) with a standard gearcase.

It serves as a direct replacement for Mercury part numbers 8M0120837 and 803748K01 (water pump components only), and Tohatsu part number 3V1-87500-0.

• Installation: Designed for a direct fit, replacing original OEM components without modification.
• Fuel Type: Compatible with gasoline engines.
• Complete Service: The kit includes a new impeller, thermostat, fuel filter, and all required gaskets and pins for a full service.

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.

For Tohatsu owners, confirm your engine model and specifications in the table below.

Technical Specifications

Package Contents

• 1 x Water Pump Impeller (Replaces Mercury 47-8037481, Tohatsu 3B2-65021-1)
• 1 x Cotter Pin (Replaces Mercury 951403-0310)
• 1 x Pin Key (Replaces Mercury 9521811, Tohatsu 3B2-65022-0)
• 1 x Pin (Replaces Mercury 951503-0318)
• 1 x Thermostat (Replaces Mercury 8M0119207, Tohatsu 3NV-01030-0)
• 1 x Thermostat Gasket (Replaces Mercury 27-8M0214960, Tohatsu 346-01032-0)
• 1 x Fuel Filter (Replaces Mercury 35-8M0157133, Tohatsu 369-02230-0)
• 1 x Drain Gasket (Replaces Mercury 12-895146, Tohatsu 3R3-07406-0)
• 2 x Drain Gaskets (Replaces Mercury 8M0075255, Tohatsu 332600060)

Installation Guide

1. Ensure the engine is off, disconnect the battery, and shut off the fuel supply.
2. Drain the lubricant from the lower unit gearcase.
3. Remove the lower unit assembly from the outboard's driveshaft housing.
4. Unbolt and carefully lift the water pump housing to expose the old impeller.
5. Note the rotational direction of the old impeller fins before removing it.
6. Remove the impeller, wear plate, key, and any gaskets.
7. Thoroughly clean all mating surfaces and inspect the housing for cracks or warping.
8. Install the new components from the kit in reverse order. Ensure the impeller key is seated correctly and fins are oriented property.
9. Locate and replace the engine thermostat and its gasket.
10. Replace the old fuel filter with the new one from the kit.
11. Reassemble the lower unit, refill with fresh gearcase oil, and reinstall it on the outboad.
12. Once assembled, start the engine at idle and confirm a steady stream of water is exiting the tell-tale port.

Troubleshooting & FAQ

How do I confirm this kit fits my Mercury engine?
This kit is specifically for Mercury and Mariner 8-9.9 HP (209cc) 4-stroke models manufactured in 2018 or later, with a serial number of 0R042475 or higher. It is critical to check your engine's serial number before purchasing to ensure compatibility.

What are the signs my water pump impeller needs replacement?
The most common symptoms of a failing impeller are the engine overheating at idle or low speeds, or a weak, inconsistent, or non-existent water stream from the tell-tale (peephole) outlet. During inspection, a damaged impeller may have cracked, brittle, or missing fins.

How often should I service the water pump?
For preventative maintenance, we recommend inspecting the water pump impeller annually and replacing it every 1-2 years or every 100-200 hours of operation, whichever occurs first. This helps prevent unexpected engine overheating and potential damage.

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.