Water Pump Impeller with Key – Fits Mercury Mariner 2-Stroke 3.9, 4, 4.5, 6, 7.5 & 9.8 HP, 0.456 in Shaft
Water Pump Impeller with Key – Fits Mercury Mariner 2-Stroke 3.9, 4, 4.5, 6, 7.5 & 9.8 HP, 0.456 in Shaft is backordered and will ship as soon as it is back in stock.
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Water Pump Impeller with Key – Fits Mercury Mariner 2-Stroke 3.9, 4...
Water Pump Impeller with Key – Fits Mercury Mariner 2-Stroke 3.9, 4, 4.5, 6, 7.5 & 9.8 HP, 0.456 in Shaft is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket water pump impeller with key is designed for selected Mercury and Mariner 2-stroke outboard applications using a 0.456-inch shaft. It is intended to restore water-pump circulation and help maintain proper engine cooling when the original impeller is worn, damaged, or due for scheduled service.
The product is supplied as one impeller with one matching key. It is not a complete water-pump service kit and does not include the pump housing, wear plate, gaskets, seals, or other water-pump components.
- Application range: Mercury and Mariner 2-stroke outboards rated 3.9, 4, 4.5, 6, 7.5, and 9.8 HP.
- Required shaft inside diameter: 0.456 inch.
- Includes the impeller and key needed for the listed application.
- Aftermarket replacement for maintenance or repair of the outboard water-pump system.
Part Number References
Use the following manufacturer and aftermarket reference numbers together with the shaft and engine details to confirm suitability before ordering.
| Brand or source | Reference number |
|---|---|
| Mercury | 47-89981 |
| Mercury | 47-89981T2 |
| Mercury | 47-65957 |
| Mercury | 47-39074 |
| Sierra | 18-3039 |
| Mallory | 9-45305 |
| GLM | 12270 |
| CEF | 500314 |
Engine Compatibility
For the listed Mercury and Mariner 2-stroke applications, verify the complete engine identification and confirm that the water-pump shaft uses the required 0.456-inch diameter. Horsepower alone is not sufficient to confirm fitment because different engines and serial ranges may use different impellers.
| Brand | Stroke | Rated horsepower | Shaft requirement | Fitment note |
|---|---|---|---|---|
| Mercury / Mariner | 2-Stroke | 3.9 HP | 0.456 in | Confirm the engine model and water-pump shaft before ordering. |
| Mercury / Mariner | 2-Stroke | 4 HP | 0.456 in | Confirm the engine model and water-pump shaft before ordering. |
| Mercury / Mariner | 2-Stroke | 4.5 HP | 0.456 in | Confirm the engine model and water-pump shaft before ordering. |
| Mercury / Mariner | 2-Stroke | 6 HP | 0.456 in | Confirm the engine model, serial range, and water-pump shaft before ordering. |
| Mercury / Mariner | 2-Stroke | 7.5 HP | 0.456 in | Confirm the engine model and water-pump shaft before ordering. |
| Mercury / Mariner | 2-Stroke | 9.8 HP | 0.456 in | Confirm the engine model and water-pump shaft before ordering. |
Technical Specifications
- Product type
- Water pump impeller with key
- Application
- Mercury and Mariner 2-stroke outboards
- Rated horsepower range
- 3.9, 4, 4.5, 6, 7.5, and 9.8 HP
- Shaft inside diameter
- 0.456 inch
- Aftermarket reference
- Sierra 18-3039
- Material
- Not specified in the product record
What's in the Box
- 1 x Water pump impeller
- 1 x Matching impeller key
Gaskets, seals, wear plates, pump housings, and other water-pump service parts are not included unless separately stated.
Installation Notes
- Confirm the engine model, stroke, serial information where applicable, and 0.456-inch shaft requirement before beginning installation.
- Remove the lower unit or gearcase according to the engine manufacturer's service procedure.
- Remove the water-pump housing and carefully extract the old impeller and key.
- Clean debris, corrosion, and damaged gasket material from the pump housing and related sealing surfaces.
- Install the supplied key and impeller in the same orientation as the original component.
- Inspect the housing, wear plate, seals, and gaskets. Replace worn or damaged components as required; replacement service parts are not included.
- Reassemble the water pump and lower unit using the manufacturer's torque specifications.
- Test the outboard in water and confirm a steady cooling-water tell-tale stream before normal operation.
Troubleshooting & FAQ
How do I confirm that this impeller fits my engine?
Confirm all of the following: Mercury or Mariner brand, 2-stroke configuration, one of the listed horsepower ratings, and a water-pump shaft with a 0.456-inch diameter. Check the engine model and serial information where applicable, then compare the old impeller and key before installation.
Does this product include a key?
Yes. The product is supplied as one water-pump impeller with one matching key.
Is this a complete water-pump repair kit?
No. This listing is for the impeller and key only. The pump housing, wear plate, gaskets, seals, and other service components are not included.
What happens if my shaft is a different size?
Do not install this impeller on a shaft that does not match the required 0.456-inch diameter. A different shaft size can cause improper fitment, poor water-pump performance, and possible engine damage.
What are common signs of a worn water-pump impeller?
Possible signs include a weak or missing tell-tale stream, overheating at idle or low speed, or a high-temperature warning. Stop operation and inspect the cooling system if any of these symptoms appear.
Is this an OEM part?
No. This is an aftermarket replacement impeller. The listed Mercury, Sierra, Mallory, GLM, and CEF numbers are reference numbers used to help identify the intended application.
Safety & Important Information
- Verify the engine model, stroke, horsepower, serial information where applicable, shaft diameter, and original impeller before purchase.
- Do not rely on horsepower alone to determine fitment.
- Follow the outboard manufacturer's service instructions and torque specifications.
- Professional installation is recommended if you are not familiar with lower-unit or water-pump service.
- Never operate the outboard without an adequate water supply for cooling.
About Sea Sierra
- Marine replacement parts — Practical aftermarket components for routine maintenance and repair.
- Application-focused fitment — Product information highlights the engine, stroke, and shaft conditions needed for selection.
- Customer support — Contact support with your engine model and serial information if you need help checking the application.
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