Water Pump Impeller – Fits Mercury/Mariner 8-20 HP Four-Stroke (Replaces 47-803748)
Water Pump Impeller – Fits Mercury/Mariner 8-20 HP Four-Stroke (Replaces 47-803748) 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 – Fits Mercury/Mariner 8-20 HP Four-Stroke (Rep...
Water Pump Impeller – Fits Mercury/Mariner 8-20 HP Four-Stroke (Replaces 47-803748) is backordered and will ship as soon as it is back in stock.
Product Details
This Water Pump Impeller – Fits Mercury/Mariner 8-20 HP Four-Stroke Outboards (Replaces 47-803748) is a crucial cooling system component designed for Mercury and Mariner 8, 9.9, 10, 15, and 20 HP four-stroke outboard motors manufactured between 2005 and 2023. It ensures proper water circulation to prevent engine overheating.
This part is a direct interchange for Mercury part numbers 47-803748, 47-8M0214944, 47-8M0135803, 47-803748002; Sierra 18-8921; and CEF Marine 500383.
- Engineered as a direct replacement for original equipment.
- Constructed from durable neoprene rubber for reliable performance.
- Includes one impeller for a complete replacement.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By |
|---|---|---|
| Mercury | 47-803748 | 47-8M0214944 |
| Mercury | 47-8M0135803 | 47-8M0214944 |
| Mercury | 47-803748002 | 47-8M0214944 |
| Sierra | 18-8921 | |
| CEF Marine | 500383 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercury and Mariner models, it is critical to verify your engine's serial number falls within the specified ranges to ensure correct fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 8 HP (209cc) | 8 | 4-Stroke | 2005–2023 | 47-803748/47-8M0214944 | Serial #: 0P325500 & Up, 0R042475 & Up |
| Mercury | 9.9 HP (209cc) | 9.9 | 4-Stroke | 2005–2023 | 47-803748/47-8M0214944 | Serial #: 0P325500 & Up, 0R042475 & Up, 0N059858 & Up |
| Mercury | 10 HP (2CYL) | 10 | 4-Stroke | 2005–2023 | 47-803748/47-8M0214944 | Serial #: 0R575531-0R833819 |
| Mercury | 15 HP (2CYL) | 15 | 4-Stroke | 2005–2023 | 47-803748/47-8M0214944 | Serial #: 0R235949-0R833819, 0N001590 & Up |
| Mercury | 15 HP Sea Pro | 15 | 4-Stroke | 2005–2023 | 47-803748/47-8M0214944 | Serial #: 0R051685-0R123564, 0R123565 & Up |
| Mercury | 18 HP (2CYL) | 18 | 4-Stroke | 2005–2023 | 47-803748/47-8M0214944 | Serial #: 0N001590-0N055284, 0N055285 & Up |
| Mercury | 20 HP (2CYL) | 20 | 4-Stroke | 2005–2023 | 47-803748/47-8M0214944 | Serial #: 0R235168-0R833819 |
| Mariner | 20 HP | 20 | 4-Stroke | 2008 | 47-803748/47-8M0214944 | Models: 7F20201ZK, 7F20211ZK, 7F20302ZK, 7F20311ZK, 7F20312ZK, 7F20411ZK, 7F20412ZK |
Technical Specs
- Product Type
- Water Pump Impeller
- Installation
- Direct replacement for original equipment
- Housing Material
- Neoprene rubber
- Housing Color
- Black
- Dimensions
- 41.2 mm diameter × 23.8 mm height (1.62 in × 0.94 in)
- Hub Shaft Diameter
- 14.0 mm (0.55 in)
- Number of Blades
- 6
- Internal Shaft Insert Diameter
- 16.03 mm
What’s in the Box
- 1 x Water Pump Impeller (47-803748/47-8M0214944)
Installation Notes
- Disconnect the engine's battery and remove the lower unit (gearcase).
- Unbolt and carefully remove the water pump housing cover.
- Observe the rotational direction of the old impeller's blades before removal.
- Remove the old impeller, key, gaskets, and wear plate.
- Thoroughly clean the inside of the pump housing and all mating surfaces.
- Lightly lubricate the new impeller and the inside of the pump housing with marine-grade silicone grease.
- Install the new wear plate, gasket, and drive key.
- Slide the new impeller onto the driveshaft while turning the shaft clockwise to correctly seat the blades.
- Reinstall the water pump housing with a new gasket and tighten bolts to the manufacturer's specified torque.
- Reattach the lower unit and test the engine's cooling system at the ramp, ensuring a steady tell-tale stream.
Troubleshooting & FAQ
How do I know if this impeller is the right one for my motor?
The best way to ensure compatibility is to check your engine's model, year, and serial number against the detailed list in our Engine & Model Compatibility table. Even if your HP and year match, serial number ranges are critical for confirming the fit.
What are the common signs of a failing water pump impeller?
Common symptoms include the engine overheating alarm sounding, a weak or non-existent water stream from the "tell-tale" outlet port, and in some cases, a steamy exhaust. Failure to replace a worn impeller can lead to severe engine damage.
How often should I replace my outboard's impeller?
As a general maintenance rule, it is recommended to replace the water pump impeller every 1 to 2 years or every 100-200 hours of operation, whichever comes first. This interval can be shorter if you frequently operate in sandy, silty, or saltwater conditions.
Is this aftermarket impeller as good as the original Mercury part?
Our aftermarket impellers are manufactured to meet or exceed OEM specifications using high-quality neoprene rubber for durability and performance. While not an OEM part, it offers a reliable and cost-effective alternative without compromising on quality.
Is any lubricant required during installation?
Yes, applying a light coat of marine-grade silicone grease or a soap-and-water mixture to the impeller blades and inside the pump housing will ease installation and prevent damage to the impeller during the first dry start.
What is the difference between OEM and aftermarket parts?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. All 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 is 5–15 days. Standard shipping is free to most regions; expedited options will appear at checkout if they are available for your location.
What is the warranty and return policy?
This part is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for parts that are unused and in their original condition. See our full policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchase. If anything differs—even if your model appears on the compatibility list—do not purchase.
- This is an aftermarket replacement component, not an Original Equipment Manufacturer (OEM) part.
- Professional installation is highly recommended for safety, proper function, and to prevent engine damage.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world conditions.
- Fast Global Fulfillment — Enjoy free standard delivery to most regions worldwide, typically within 5–15 days.
- Manufacturer-Direct Value — We offer fair pricing by eliminating intermediaries, without ever compromising on materials or quality control.
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