Water Pump Impeller Kit – Fits Mercury/Mariner 8–9.9 HP 4-Stroke 209cc (Replaces 8M0120837, 803748K01, 3V1-87500-0)
Water Pump Impeller Kit – Fits Mercury/Mariner 8–9.9 HP 4-Stroke 209cc (Replaces 8M0120837, 803748K01, 3V1-87500-0) is backordered and will ship as soon as it is back in stock.
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Water Pump Impeller Kit – Fits Mercury/Mariner 8–9.9 HP 4-Stroke 20...
Water Pump Impeller Kit – Fits Mercury/Mariner 8–9.9 HP 4-Stroke 209cc (Replaces 8M0120837, 803748K01, 3V1-87500-0) is backordered and will ship as soon as it is back in stock.
Product Details
This Water Pump Impeller Kit for Mercury/Mariner 8–9.9 HP 4-stroke 209cc outboard motors is a multi-component maintenance kit intended to service the water pump and related cooling-system components. It is designed for applicable Mercury, Mariner, and Tohatsu outboards using the specified standard gearcase configuration.
The kit is listed as a replacement for OEM reference numbers Mercury 8M0120837, Mercury 803748K01, and Tohatsu 3V1-87500-0. Confirm the engine model, year, serial number, gearcase configuration, and the original component numbers before ordering.
- Aftermarket replacement kit for water-pump and routine marine-engine maintenance.
- Includes an impeller, keying hardware, thermostat, gaskets, and fuel-filter components as listed below.
- Designed for gasoline-fueled 4-stroke outboard applications covered by the fitment information below.
Part Number Matrix
Use these references as cross-reference leads and verify them against the number and configuration of the component being replaced.
| Brand | Part Number | Notes |
|---|---|---|
| Mercury | 8M0120837 | Primary product reference |
| Mercury | 803748K01 | Water-pump reference |
| Tohatsu | 3V1-87500-0 | Product cross-reference |
Engine & Model Compatibility
Fitment must be confirmed using the complete engine conditions, including brand, horsepower, 4-stroke configuration, model, year, serial number, and gearcase type.
For Mercury and Mariner applications, the supplied fitment information identifies 8 and 9.9 HP 4-stroke models from 2018 and newer with serial number 0R042475 and above and a standard gearcase.
For Tohatsu applications, the supplied fitment information identifies 209cc 4-stroke models including MFS8, MFS9.8B, and MFS6BZ. Verify the exact model and year before installation.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury/Mariner | F8/F9.9 | 8–9.9 | 4-Stroke | 2018+ | 8M0120837 | Standard gearcase; S/N 0R042475 and above |
| Tohatsu | MFS8 | 8 | 4-Stroke | Not specified | 3V1-87500-0 | 209cc; verify exact model and year |
| Tohatsu | MFS9.8B | 9.8 | 4-Stroke | Not specified | 3V1-87500-0 | 209cc; verify exact model and year |
| Tohatsu | MFS6BZ | 6 | 4-Stroke | Not specified | 3V1-87500-0 | 209cc; verify exact model and year |
Technical Specs
- Product Type
- Aftermarket outboard maintenance service kit with water-pump impeller components
- Application
- Gasoline-fueled 4-stroke outboard motors
- Nominal Engine Range
- 6–9.9 HP applications listed above; confirm exact fitment before purchase
- Impeller Material
- Rubber
- Installation
- Replacement installation; follow the engine manufacturer's service procedures
What’s in the Box
- 1 × Water pump impeller — replaces Mercury 47-8037481 and Tohatsu 3B2-65021-1
- 1 × Cotter pin — replaces Mercury 951403-0310
- 1 × Pin key — replaces Mercury 9521811 and Tohatsu 3B2-65022-0
- 1 × Pin — replaces Mercury 951503-0318
- 1 × Thermostat — replaces Mercury 8M0119207 and Tohatsu 3NV-01030-0
- 1 × Thermostat gasket — replaces Mercury 27-8M0214960 and Tohatsu 346-01032-0
- 1 × Fuel filter — replaces Mercury 35-8M0157133 and Tohatsu 369-02230-0
- 1 × Drain gasket — replaces Mercury 12-895146 and Tohatsu 3R3-07406-0
- 2 × Drain gaskets — replaces Mercury 8M0075255 and Tohatsu 332600060
Installation Notes
- Turn the engine off, place it in neutral, and disconnect the battery before beginning service.
- Remove the lower unit or gearcase according to the engine manufacturer's service procedure.
- Remove the water-pump housing cover to access the impeller.
- Record the original impeller-vane direction and retain the original key as a reference before removal.
- Clean debris and corrosion from the housing interior, wear plate, and related sealing surfaces.
- Install the new key and impeller, rotating the impeller in the correct direction so the vanes seat without damage.
- Replace the applicable gaskets and reassemble the pump housing. Tighten fasteners to the manufacturer's specifications.
- Replace the thermostat and thermostat gasket if required for the applicable engine service.
- Reinstall the lower unit, reconnect the battery, and test the engine in water. Confirm a steady tell-tale stream and normal operating temperature.
Troubleshooting & FAQ
How do I confirm this kit fits my motor?
Verify the engine brand, model, horsepower, 4-stroke configuration, year, serial number, gearcase type, and the original component numbers. Mercury and Mariner applications listed here require particular attention to the 2018-and-newer range and serial number 0R042475 or above. Do not rely on horsepower alone.
What are the signs of a failing water-pump impeller?
Common symptoms include a weak or absent tell-tale stream, an overheating warning, elevated operating temperature, or reduced engine performance. Cracked, brittle, deformed, or missing impeller vanes also indicate that service is required.
How often should the water-pump impeller be replaced?
Inspect the impeller during scheduled maintenance and replace it when the manufacturer's service interval or its condition requires. Frequent operation in sandy, silty, or saltwater conditions may require more frequent inspection.
My engine still overheats after installing the kit. What should I check?
Check the impeller installation, key, pump housing, wear plate, gaskets, water-intake passages, cooling-water passages, tell-tale outlet, thermostat, and temperature-sensor system. If the cause is not apparent, have the engine inspected by a qualified marine technician.
Why does the kit include a fuel filter and thermostat?
The listed product contents combine water-pump service components with other routine maintenance components. Confirm that each included component matches the service requirements of your specific engine before installation.
Is this an OEM part or aftermarket?
This listing is for an aftermarket replacement kit, not an original-equipment-manufacturer component. The OEM and manufacturer numbers shown are reference numbers for identification and cross-reference purposes.
What are the shipping speed and cost?
Shipping availability, delivery estimates, and cost are shown at checkout and may vary by destination and service level.
What is the warranty and return policy?
Warranty coverage and return eligibility are governed by the current store policies. Review the applicable policy before purchase and contact support if assistance is needed.
Safety & Important Info
- Confirm the engine model, year, serial number, stroke, gearcase, and original part references before purchase.
- Compare the supplied parts with the original components before installation. Do not install a component that differs in size, design, or application.
- This is an aftermarket replacement kit and is not an original equipment manufacturer product.
- Follow the engine manufacturer's service instructions and torque specifications. Professional installation is recommended when lower-unit or cooling-system service is unfamiliar.
- Never operate the engine without adequate cooling-water supply, and stop immediately if overheating or an abnormal tell-tale stream occurs.
About Sea Sierra
- Pro-Grade Standards — We supply marine replacement parts selected for dependable service in real-world operating conditions.
- Fast Global Fulfillment — Shipping options and delivery estimates are provided at checkout for the destination and service selected.
- Manufacturer-Direct Value — We work with manufacturing partners to provide practical replacement solutions for marine maintenance.
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