Water Pump Impeller Kit – Fits Yamaha 20D/25D/25N 2-Stroke Outboards (Replaces Yamaha 6L2-W0078-00-00, Sierra 18-3431, Mercury 879137)
Water Pump Impeller Kit – Fits Yamaha 20D/25D/25N 2-Stroke Outboards (Replaces Yamaha 6L2-W0078-00-00, Sierra 18-3431, Mercury 879137) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
International delivery times may vary due to customs processing.
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Water Pump Impeller Kit – Fits Yamaha 20D/25D/25N 2-Stroke Outboard...
Water Pump Impeller Kit – Fits Yamaha 20D/25D/25N 2-Stroke Outboards (Replaces Yamaha 6L2-W0078-00-00, Sierra 18-3431, Mercury 879137) is backordered and will ship as soon as it is back in stock.
Product Details
This Water Pump Impeller Kit – Fits Yamaha 20D/25D/25N 2-Stroke Outboards (Replaces 6L2-W0078-00-00) is designed for Yamaha 2-stroke 20HP and 25HP outboards manufactured between 1988–2004, including the 20D, 25D, and 25N models. This kit provides all necessary components to restore your engine's cooling system performance.
It serves as a direct replacement for Yamaha 6L2-W0078-00-00, Sierra 18-3431, and Mercury 879137, ensuring a precise fit and function.
- Engineered for a drop-in installation.
- The kit provides essential components for a water pump rebuild but does not include the pump housing.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 6L2-W0078-00-00 |
| Sierra | 18-3431 |
| Mercury | 879137 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | 20D | 20 | 2-Stroke | 1996–1997 | 6L2-W0078-00-00 | |
| Yamaha | 25D/25N | 25 | 2-Stroke | 1988–1998, 2000, 2003–2004 | 6L2-W0078-00-00 |
Technical Specs
- Product Type
- Water Pump Impeller Kit
- Installation
- Drop-in replacement
- Other Technical Attributes
- Does not include pump housing
What’s in the Box
- 1 x Cartridge Outer Plate (6L2-44323-00-00)
- 1 x O-Ring (93210-45161-00)
- 1 x Impeller (6L2-44352-00-00)
- 1 x Cartridge Insert (6L2-44322-00-00)
- 4 x Bolts (97095-06040-00)
- 1 x Woodruff Key (90280-03024-00)
- 4 x Washers (92990-06600-00)
Installation Notes
- Disconnect the battery and remove the engine cover. Disconnect the shift linkage from the lower unit.
- Remove the bolts securing the lower unit (gearcase) to the upper casing and carefully lower it.
- Unbolt and remove the water pump housing to expose the old impeller. Note the direction of the old impeller's vanes.
- Clean the housing interior and inspect the insert and base plate for wear, replacing if necessary.
- Install the new Woodruff key into the driveshaft slot. Align the new impeller with the key and slide it down.
- Apply a light coat of marine grease or soap-and-water solution to the inside of the housing and on the impeller.
- Install the new impeller, turning the driveshaft clockwise to bed the vanes correctly inside the housing.
- Reinstall the water pump housing, outer plate, and any new gaskets/O-rings provided. Tighten bolts to manufacturer specifications.
- Reattach the lower unit to the engine, reconnect the shift linkage, and test the engine in water to verify proper water flow.
Troubleshooting & FAQ
How do I know if this kit fits my engine?
This kit is specifically for Yamaha 2-stroke 20HP and 25HP outboards (models 20D, 25D, 25N) from 1988–2004. Please verify your engine model and year of manufacture against the 'Engine & Model Compatibility' table. Do not purchase if your model is not listed.
Does this kit include the water pump housing?
No, this is an impeller repair kit and does not include the metal or plastic pump housing. It includes the impeller and associated gaskets, plates, and hardware required for a standard replacement.
What are the signs of a failing water pump impeller?
Common symptoms include a weak or intermittent water stream from the "telltale" outlet, engine overheating alerts, and, in severe cases, steam from the exhaust. Reduced water pressure is the first sign of a worn impeller.
How often should I replace my outboard's impeller?
For most recreational boaters, it is recommended to replace the water pump impeller every 1-2 years or every 100-200 hours of operation, whichever comes first. Refer to your engine's service manual for specific maintenance intervals.
Can I install this kit myself?
While installation is possible for those with mechanical experience, we recommend professional installation to ensure safety and correct function. The process involves removing the lower unit, which can be complex. Incorrect installation can lead to engine damage from overheating.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
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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