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

$42.00 $67.00

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Water Pump Impeller Kit – Fits Mercury/Mariner 8-9.9 HP 4-Stroke 209cc (Replaces 8M0120837, 3V1-87500-0) is backordered and will ship as soon as it is back in stock.

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You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

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Delivery and Shipping

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 Mercury/Mariner 8-9.9 HP 4-Stroke 209cc is a comprehensive service kit designed to restore the cooling system on Mercury, Mariner, and Tohatsu 8-9.9 HP 4-stroke 209cc outboard motors (2018 and newer, S/N 0R042475 and above) with a standard gearcase.

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

Engineered as a direct OEM-equivalent replacement for seamless installation.
Includes all essential components for a complete water pump and thermostat service.
Designed for use in gasoline-fueled 4-stroke outboard marine engines.

Part Number Matrix

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

Brand	Part Number	Notes
Mercury	8M0120837
Mercury	803748K01	Water pump kit only
Tohatsu	3V1-87500-0

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury/Mariner engines, this kit fits 8 and 9.9 HP 4-stroke models from 2018 and newer with serial number 0R042475 and up, designed for standard gearcases.

For Tohatsu engines, this kit is compatible with 209cc models including the MFS8, MFS9.8B, and MFS6BZ. Please verify specific years if possible.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	F8/F9.9	8-9.9	4-Stroke	2018+	8M0120837	Standard gearcase only, S/N 0R042475 and above
Tohatsu	MFS8	8	4-Stroke		3V1-87500-0	209cc
Tohatsu	MFS9.8B	9.8	4-Stroke		3V1-87500-0	209cc
Tohatsu	MFS6BZ	6	4-Stroke		3V1-87500-0	209cc

Technical Specs

Product Type: Outboard Motor Maintenance Kit / Water Pump Impeller Kit
Installation: Direct OEM replacement
Fuel Type: Gasoline
Housing Material: Rubber (impeller)

What’s in the Box

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 Notes

Ensure the engine is off, in neutral, and the battery is disconnected.
Remove the lower unit (gearcase) from the outboard's midsection by unbolting it.
Unbolt and remove the water pump housing cover to access the impeller.
Take note of the old impeller's vane direction before removing it and the key.
Clean any debris or corrosion from the housing interior and wear plate.
Install the new key and slide the new impeller into place, twisting it clockwise to seat the vanes correctly.
Replace the gaskets and reassemble the pump housing, ensuring bolts are torqued to spec.
Replace the thermostat and its gasket in the engine block.
Reinstall the lower unit, reconnect the battery, and test operation in water, confirming a steady stream from the tell-tale.

Troubleshooting & FAQ

How do I confirm this kit fits my motor?

Verify your engine's brand (Mercury/Mariner/Tohatsu), horsepower (8-9.9 HP), and year (2018+ for Mercury). For Mercury motors, you must also confirm your serial number is 0R042475 or higher. Cross-referencing the OEM part numbers listed in the "Part Number Matrix" is the most reliable method.

What are the signs of a failing water pump impeller?

Common symptoms include a weak or non-existent water stream from the engine's tell-tale (water outlet), engine overheating alarms, and reduced engine performance. Visible damage to the old impeller, such as cracked, brittle, or missing vanes, also indicates failure.

How often should the water pump impeller be replaced?

As a general maintenance rule, it is recommended to inspect the impeller annually and replace it every 1-2 years or every 100-200 hours of operation, whichever comes first. This interval can be shorter if you operate in sandy, silty, or saltwater conditions.

My engine still overheats after installing the new kit. What's next?

This kit includes a new thermostat, which is a common cause of overheating. If the problem persists, check for blockages in the cooling water passages, intake screens, or the tell-tale outlet. A faulty temperature sensor or gauge could also be the culprit.

Why does this kit include a fuel filter and thermostat?

This is a comprehensive maintenance kit. The thermostat is a critical part of the cooling system, and the fuel filter is a key preventative maintenance item often replaced at the same service interval as the water pump to ensure engine reliability.

Is this an OEM part or aftermarket?

This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials and manufactured in an ISO 9002 facility, with batch inspections for consistency.

What are the shipping speed and cost?

We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free, and expedited options will appear at checkout where available.

What is the warranty and return policy?

This product is covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. See our policy page or reach out for instructions.

Safety & Important Info

Verify the images and specifications against your original part before purchase. If anything differs—even if your model appears on a compatibility list—do not proceed with the purchase.
This is an aftermarket replacement part, not an original equipment manufacturer (OEM) component.
Professional installation is strongly recommended for safety, proper function, and to prevent engine damage.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and continuously tested for real-world conditions.
Fast Global Fulfillment — We offer free standard delivery to most regions with a typical transit time of 5–15 days.
Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.

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