Water Pump Impeller – Fits Mercury/Mariner 10-40 HP (Replaces 47-20813)
Water Pump Impeller – Fits Mercury/Mariner 10-40 HP (Replaces 47-20813) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
Worry-free returns
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.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Water Pump Impeller – Fits Mercury/Mariner 10-40 HP (Replaces 47-20...
Product Details
This replacement Water Pump Impeller fits Mercury/Mariner 10-40 HP 2-stroke outboard engines, primarily from the 1970s and 1980s. It is a critical component for maintaining proper engine cooling by ensuring consistent water flow through the system.
It serves as a direct interchange for Sierra 18-3008 and Mercury part numbers 47-20813 and 47-25287.
- Installs as a direct replacement for the original part.
- Made from a durable rubber/neoprene compound suitable for marine environments.
- Features a curved blade design for efficient water transfer.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 47-20813 |
| Mercury | 47-25287 |
| Sierra | 18-3008 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This impeller is designed for a range of vintage Mercury and Mariner outboards. Please verify your engine's serial number or model against this list, as year ranges can vary.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. |
|---|---|---|---|---|---|
| Mercury | MARK 15 | 15 | 2-Stroke | 47-20813 | |
| Mercury | MARK 20 | 20 | 2-Stroke | 47-20813 | |
| Mercury | MARK 25 | 25 | 2-Stroke | 47-20813 | |
| Mercury | MARK 25E | 25 | 2-Stroke | 47-20813 | |
| Mercury | MARK 30 | 30 | 2-Stroke | 47-20813 | |
| Mercury | MARK 30E | 30 | 2-Stroke | 47-20813 | |
| Mercury | 16 HP | 16 | 2-Stroke | Serial 700000-Up | 47-20813 |
| Mercury | 40 HP | 40 | 2-Stroke | Serial 941751–1224480 | 47-20813 |
| Mercury | KH7 | 2-Stroke | 47-20813 | ||
| Mercury | WG7 | 2-Stroke | 47-20813 |
Technical Specs
- Product Type
- Water Pump Impeller
- Installation
- Direct replacement
- Housing Material
- Rubber/Neoprene
- Design
- Curved blades design for efficient water transfer
- Dimensions
- 5.13" H x 4.0" W x 0.88" L
What’s in the Box
- 1 x Water Pump Impeller (Replaces 47-20813)
Installation Notes
- Disconnect the negative battery terminal and ensure the engine is off and cool.
- Place a drain pan under the lower unit and remove it from the outboard motor.
- Unscrew the bolts holding the water pump housing cover and remove the cover.
- Carefully note the rotational direction of the existing impeller blades before removing the old impeller and gasket.
- Thoroughly clean the inside of the pump housing and all mating surfaces.
- Install the new gasket and apply a light coat of marine grease to the inside of the housing.
- Slide the new impeller onto the driveshaft while turning the shaft clockwise to correctly bend the blades.
- Reinstall the water pump housing cover and tighten the bolts to the manufacturer's specified torque.
- Reattach the lower unit to the outboard, ensuring all connections are secure.
- Start the engine in a water test tank or on the water to verify a strong, steady stream from the tell-tale outlet.
Troubleshooting & FAQ
How do I find out if this impeller fits my engine?
This impeller is made for select Mercury and Mariner 2-stroke outboards from 10–40 HP, especially vintage models. To confirm fitment, check your engine model or serial number against the compatibility table or match your existing part number to one of the cross-references listed (e.g., 47-20813, 18-3008).
What are the signs of a faulty water pump impeller?
A failing impeller typically causes the engine to overheat. Other signs include a weak or nonexistent water stream from the "tell-tale" indicator outlet, or steam coming from the exhaust.
What is the recommended replacement interval for this part?
As a general rule, impellers should be inspected annually and replaced every 1-2 years or after every 100 hours of use. If you boat in saltwater or silty conditions, more frequent replacement is advised to prevent cooling system failure.
What causes an impeller to fail prematurely?
The most common cause of immediate failure is running the engine out of water, which instantly burns the rubber. Other causes include sucking up sand or debris, chemical degradation from fuel/oil, and old age, which makes the rubber brittle and prone to cracking.
OEM vs. Aftermarket: What's the difference?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. Our parts are manufactured in an ISO 9002 facility and are batch-inspected for quality and consistency.
How fast is shipping and what does it cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
What is the warranty and return policy?
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
Payment & Security
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