Water Pump Impeller for Mercury 8/9.9 HP 4-Stroke and Tohatsu/Nissan 6/8/9.8 HP Outboards – Replaces 47-8037481, 3B2-65021-1
Water Pump Impeller for Mercury 8/9.9 HP 4-Stroke and Tohatsu/Nissan 6/8/9.8 HP Outboards – Replaces 47-8037481, 3B2-65021-1 is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Water Pump Impeller for Mercury 8/9.9 HP 4-Stroke and Tohatsu/Nissa...
Water Pump Impeller for Mercury 8/9.9 HP 4-Stroke and Tohatsu/Nissan 6/8/9.8 HP Outboards – Replaces 47-8037481, 3B2-65021-1 is backordered and will ship as soon as it is back in stock.
Product Details
This replacement water pump impeller is designed for selected Mercury, Tohatsu, and Nissan outboard cooling systems. It is a single impeller supplied for installation in the lower-unit water pump assembly.
Company fitment data identifies this impeller for Mercury 8 HP and 9.9 HP 4-stroke engines, including the 209 cc configuration, as well as Tohatsu/Nissan 6 HP, 8 HP, and 9.8 HP 2-stroke engines. It is also listed for Tohatsu MFS8 and MFS9.8 4-stroke models. Always compare the part number and the original impeller before ordering.
- Replacement water pump impeller for selected small outboard engines.
- Installs in the lower-unit water pump assembly.
- Sold as one impeller; the square drive key is not included.
- Aftermarket replacement component, not a manufacturer-branded OEM part.
Part Number References
Use the following manufacturer and aftermarket references to help compare your original part. A matching number should be confirmed together with the engine model, horsepower, stroke, and year or serial-number requirements.
| Brand or Source | Reference Number | Reference Type |
|---|---|---|
| Tohatsu | 3B2-65021-1 | Manufacturer reference |
| Tohatsu | 3B2650211M | Manufacturer reference |
| Mercury Marine | 47-8037481 | Manufacturer reference |
| Mercury Marine | 47-803748-1 | Manufacturer reference variation |
| Mercury Marine | 8037481 | Reference number |
| Mercury Marine | 8M0214945 | Reference number |
| Sierra | 18-8920 | Aftermarket reference |
| OMC / Evinrude Johnson | 5040525 | Additional reference listed in company data |
| Sierra | 18-3086 | Catalog cross-reference |
| CEF | 500344 | Catalog cross-reference |
| Mallory | 9-45210 | Catalog cross-reference |
Engine Compatibility
The fitment below combines the exact company product records with compatible catalog applications. It is not an exhaustive list of every engine variation. Confirm the complete model designation and serial-number range for your engine before installation.
| Brand | Engine or Model Family | Rated HP | Stroke | Reference | Fitment Notes |
|---|---|---|---|---|---|
| Mercury | 8 HP and 9.9 HP, including 209 cc models | 8/9.9 HP | 4-Stroke | 47-8037481; 47-803748-1 | Company-listed Mercury fitment. Confirm the exact model and serial range. |
| Tohatsu | M6/M8/M9.8B | 6/8/9.8 HP | 2-Stroke | 3B2-65021-1 | Catalog applications include model years 2013–2022; exact serial conditions may vary. |
| Tohatsu | MFS6/MFS8/MFS9.8 and MFS8/MFS9.8A3 | 6/8/9.8 HP | 4-Stroke | 3B2-65021-1 | Company-listed MFS8/MFS9.8 fitment; catalog applications include multiple model-year variants. |
| Nissan | Selected 6/8/9.8 HP outboards sharing the listed application | 6/8/9.8 HP | 2-Stroke | 3B2-65021-1 | Company-listed Nissan/Tohatsu application. Verify the original impeller and model details. |
Technical Information
- Product Type
- Water pump impeller
- Product Construction
- Rubber impeller with a driveshaft hub
- Installation Location
- Lower-unit water pump assembly
- Quantity
- One impeller
- Drive Key
- Not included; reuse or replace the key separately if required by the engine manufacturer
- Brand Status
- Aftermarket replacement component
What's in the Box
- 1 x Water pump impeller
Not included: square drive key, water pump housing, gaskets, seals, or other lower-unit service parts.
Installation Notes
- Refer to the engine service manual and place the engine in a safe, stable position before beginning work.
- Disconnect the battery or ignition power as appropriate and prevent accidental starting.
- Remove the lower unit according to the manufacturer's procedure.
- Open the water pump housing and remove the old impeller. Note the position of the drive key and the direction of the vanes.
- Inspect the housing, wear plate, seals, and drive key for wear or damage. Replace damaged parts before reassembly.
- Install the correct key if required, then fit the new impeller onto the driveshaft. Use a suitable lubricant recommended for water-pump service.
- Reinstall the water pump housing and any gaskets or seals in the correct positions.
- Reattach the lower unit and tighten all fasteners to the service-manual specifications.
- Run the engine only in an appropriate test tank or in the water. Confirm a steady cooling-water tell-tale stream and check for overheating or leaks.
Troubleshooting & FAQ
How do I confirm fitment?
Compare your original impeller or service-manual number with the references listed above, then verify the complete engine brand, model, horsepower, stroke, year, and serial-number range. Do not rely on horsepower alone.
What are the signs of a worn impeller?
Common signs include a weak or intermittent tell-tale stream, overheating, reduced cooling-water flow, cracked or stiff vanes, missing vane material, or an impeller that has taken a permanent set.
Does this product include the square key?
No. The company product record identifies this as a single impeller, not a kit. The drive key is not included and must be reused or sourced separately when required.
Is this an OEM part?
No. This is an aftermarket replacement impeller. The manufacturer and aftermarket numbers shown on this page are reference numbers used for fitment comparison.
How often should an impeller be replaced?
Follow the maintenance interval in your engine manufacturer's service manual. Inspect the impeller regularly and replace it sooner if the engine has been operated in sandy, silty, or debris-filled water or if cooling-water flow declines.
Safety & Important Information
- Confirm the exact engine application before purchase and installation.
- Keep horsepower, stroke, model, year, and serial-number conditions together when checking compatibility.
- Do not operate an outboard without adequate cooling-water supply.
- Replace damaged gaskets, seals, wear plates, or drive keys as needed during water-pump service.
- Professional installation is recommended if you are unfamiliar with lower-unit or water-pump service.
About Sea Sierra
- Marine Replacement Parts — Practical replacement components for routine outboard maintenance and repair.
- Application-Focused Listings — Product references and fitment information are provided to help you compare the original part.
- Value for Maintenance — Aftermarket components for keeping essential marine systems in service.
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