Water Pump Impeller with Drive Key – Mercury/Mariner 2-Stroke 15–30 HP & 4-Stroke 8–50 HP
Water Pump Impeller with Drive Key – Mercury/Mariner 2-Stroke 15–30 HP & 4-Stroke 8–50 HP is backordered and will ship as soon as it is back in stock.
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Water Pump Impeller with Drive Key – Mercury/Mariner 2-Stroke 15–30...
Water Pump Impeller with Drive Key – Mercury/Mariner 2-Stroke 15–30 HP & 4-Stroke 8–50 HP is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket water pump impeller with drive key is designed for selected Mercury and Mariner outboards. It is listed for 2-stroke 15–30 HP applications and specific 4-stroke models from 8 HP through 50 HP. The impeller helps maintain the engine cooling-water flow when installed in a matching water-pump assembly.
This replacement is cross-referenced to Mercury manufacturer part numbers 47-85089-3, 47-85089-10, 47-85089, and 47-8508910. The aftermarket reference is Sierra 18-3057.
- Aftermarket water pump impeller for selected Mercury and Mariner outboards.
- Includes one drive key for the listed application.
- Verify the engine model, horsepower, stroke, and original impeller number before ordering.
Part Number Matrix
Use the following references to compare the replacement with the number on your original impeller or service parts documentation.
| Reference type | Part number |
|---|---|
| Mercury manufacturer reference | 47-85089-3 |
| Mercury manufacturer reference | 47-85089-10 |
| Mercury manufacturer reference | 47-85089 |
| Mercury manufacturer reference | 47-8508910 |
| Sierra aftermarket reference | 18-3057 |
Engine & Model Compatibility
Company fitment data covers the following Mercury and Mariner application groups. Model, year, serial number, and stroke conditions must be checked together against the engine manufacturer's parts information.
| Brand | Stroke | Rated horsepower | Listed model or application |
|---|---|---|---|
| Mercury / Mariner | 2-Stroke | 15–30 HP | Selected 15–30 HP applications |
| Mercury / Mariner | 4-Stroke | 8 HP | Bodensee, international model |
| Mercury / Mariner | 4-Stroke | 9.9 HP | 323 cc model |
| Mercury / Mariner | 4-Stroke | 13.5 HP | International model |
| Mercury / Mariner | 4-Stroke | 15 HP | Selected 15 HP applications |
| Mercury / Mariner | 4-Stroke | 25 HP | Selected 25 HP applications |
| Mercury / Mariner | 4-Stroke | 30 HP | Selected 30 HP applications |
| Mercury / Mariner | 4-Stroke | 30 HP | EFI, 3-cylinder |
| Mercury / Mariner | 4-Stroke | 40 HP | Selected 40 HP applications |
| Mercury / Mariner | 4-Stroke | 40 HP | Carbureted, 3-cylinder |
| Mercury / Mariner | 4-Stroke | 40 HP | EFI, 3-cylinder |
| Mercury / Mariner | 4-Stroke | 40 HP | Italy-market model |
| Mercury / Mariner | 4-Stroke | 45 HP | Bodensee model |
| Mercury / Mariner | 4-Stroke | 50 HP | 50 and Bigfoot applications |
Technical Specifications
- Product type
- Aftermarket water pump impeller with drive key
- Application
- Selected Mercury and Mariner 2-stroke and 4-stroke outboards
- 2-stroke fitment range
- 15–30 HP applications listed by the company catalog
- 4-stroke fitment range
- Specific 8–50 HP applications listed by the company catalog
- Aftermarket reference
- Sierra 18-3057
- Included drive key
- Yes
What's in the Box
- 1 x Water pump impeller
- 1 x Drive key
Installation Notes
- Confirm the engine model, horsepower, stroke, serial range, and original impeller reference before beginning work.
- Disconnect the battery and follow the engine manufacturer's service procedure for removing the lower unit.
- Locate the water-pump housing and remove its cover.
- Remove the old impeller and retain the drive key only if it is being replaced or reused according to the service instructions.
- Clean the housing and inspect the cover, wear surfaces, seals, and drive-shaft keyway for damage or excessive wear.
- Install the supplied drive key in the shaft keyway and fit the new impeller, aligning the hub with the key.
- Reassemble the water-pump housing and lower unit using the manufacturer's torque sequence and sealing requirements.
- Test the engine with an appropriate water supply and confirm normal cooling-water flow before operating the boat.
Troubleshooting & FAQ
How do I confirm fitment?
Compare your original impeller number with the Part Number Matrix, then confirm the engine brand, exact model, horsepower, stroke, year, and serial number. A horsepower-only match is not sufficient because water-pump designs can vary within the same horsepower range.
What are common signs of a worn impeller?
Possible signs include weak or missing telltale water flow, overheating warnings, reduced cooling performance, damaged vanes, cracks, or a visibly hardened impeller. Inspect the complete water-pump assembly when replacing the impeller.
Does this product include the drive key?
Yes. This product is listed by the company catalog as an impeller with key and includes one drive key.
Is this an OEM part?
No. This is an aftermarket replacement. The manufacturer references shown on this page are provided for application and part-number comparison only.
Should I replace the water-pump housing at the same time?
Inspect the housing, cover, wear surfaces, seals, and keyway during installation. Replace any worn or damaged components according to the engine manufacturer's service instructions.
Safety & Important Information
- Fitment is limited to the listed Mercury and Mariner application groups; do not rely on horsepower alone.
- Check the original part number and compare the replacement's hub and overall dimensions before installation.
- Follow the engine manufacturer's service manual for lower-unit removal, torque values, sealing compounds, and testing procedures.
- This is an aftermarket replacement and is not manufactured by Mercury, Mariner, or Sierra.
- Professional installation is recommended if you are not familiar with outboard lower-unit service.
About Sea Sierra
- Marine replacement parts — Practical aftermarket components for routine service and repair.
- Application-focused listings — Product references and fitment details are provided to help match the correct part.
- Service-minded support — Contact support with your engine model and serial number when additional fitment information is needed.
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