Water Pump Impeller Kit – Fits Yamaha 25-40 HP 4-Stroke (Replaces 66T-W0078-00-00)
Water Pump Impeller Kit – Fits Yamaha 25-40 HP 4-Stroke (Replaces 66T-W0078-00-00) 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 Kit – Fits Yamaha 25-40 HP 4-Stroke (Replaces 6...
Water Pump Impeller Kit – Fits Yamaha 25-40 HP 4-Stroke (Replaces 66T-W0078-00-00) is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket Water Pump Impeller Kit – Fits Yamaha 25-40 HP 4-Stroke (Replaces 66T-W0078-00-00) provides a complete solution for servicing your outboard's cooling system. It is designed for a precise fit on Yamaha 4-stroke models including 25 HP (T25) from 2001–2016, 30 HP (F30) from 2001–2005, and 40 HP (F40) from 2000–2009, as well as select 40 HP 2-stroke models.
It directly replaces Yamaha OEM part numbers 66T-W0078-00-00, 66T-W0078-01-00, and 66T-W0078-A0, along with Sierra equivalents 18-3413 / 18-3440 and Mallory 9-48610.
- Engineered for direct OEM replacement installation.
- Includes the pump housing for a comprehensive service.
- Features a durable 6-blade neoprene impeller for reliable performance.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Yamaha | 66T-W0078-00-00 | Original Equipment Manufacturer |
| Yamaha | 66T-W0078-01-00 | Superseded Part |
| Yamaha | 66T-W0078-A0 | Superseded Part |
| Sierra | 18-3413 | Aftermarket Interchange |
| Sierra | 18-3440 | Aftermarket Interchange |
| Mallory | 9-48610 | Aftermarket Interchange |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | T25 | 25 | 4-Stroke | 2001–2006 | 66T-W0078-00-00 | |
| Yamaha | T25TLR | 25 | 4-Stroke | 2001–2006 | 66T-W0078-00-00 | |
| Yamaha | T25LA | 25 | 4-Stroke | 2009–2016 | 66T-W0078-00-00 | |
| Yamaha | F30A | 30 | 4-Stroke | 2001–2005 | 66T-W0078-00-00 | |
| Yamaha | F30TLR | 30 | 4-Stroke | 2001–2005 | 66T-W0078-00-00 | |
| Yamaha | F40B | 40 | 4-Stroke | 2000–2009 | 66T-W0078-00-00 | |
| Yamaha | F40BEJR | 40 | 4-Stroke | 2004–2007 | 66T-W0078-00-00 | |
| Yamaha | F40BMJH | 40 | 4-Stroke | 2004–2007 | 66T-W0078-00-00 | |
| Yamaha | F40BMLH | 40 | 4-Stroke | 2004–2008 | 66T-W0078-00-00 | |
| Yamaha | F40BTLR | 40 | 4-Stroke | 2004–2008 | 66T-W0078-00-00 | |
| Yamaha | F40EJR | 40 | 4-Stroke | 2004–2006 | 66T-W0078-00-00 | |
| Yamaha | F40EJRB | 40 | 4-Stroke | 2003 | 66T-W0078-00-00 | |
| Yamaha | F40EJRC | 40 | 4-Stroke | 2004 | 66T-W0078-00-00 | |
| Yamaha | F40EJRD | 40 | 4-Stroke | 2005 | 66T-W0078-00-00 | |
| Yamaha | F40ESRA | 40 | 4-Stroke | 2002 | 66T-W0078-00-00 | |
| Yamaha | F40ESRB | 40 | 4-Stroke | 2003 | 66T-W0078-00-00 | |
| Yamaha | F40ESRY | 40 | 4-Stroke | 2000 | 66T-W0078-00-00 | |
| Yamaha | F40ESRZ | 40 | 4-Stroke | 2001 | 66T-W0078-00-00 | |
| Yamaha | F40MJH | 40 | 4-Stroke | 2002–2006 | 66T-W0078-00-00 | |
| Yamaha | F40MLH | 40 | 4-Stroke | 2000–2006 | 66T-W0078-00-00 | |
| Yamaha | F40MSH | 40 | 4-Stroke | 2000–2006 | 66T-W0078-00-00 | |
| Yamaha | F40TLR | 40 | 4-Stroke | 2000–2006 | 66T-W0078-00-00 | |
| Yamaha | 40X | 40 | 2-Stroke | From 1998 | 66T-W0078-00-00 | Also fits select 2-stroke models |
| Yamaha | 40XWT | 40 | 2-Stroke | From 1998 | 66T-W0078-00-00 | Also fits select 2-stroke models |
| Yamaha | E40X | 40 | 2-Stroke | From 1998 | 66T-W0078-00-00 | Also fits select 2-stroke models |
Technical Specs
- Product Type
- Water Pump Impeller Kit with Housing
- Installation
- Direct OEM Replacement
- Impeller Material
- Neoprene Rubber
- Impeller Design
- 6-Blade
- Shaft Size
- 16 mm
- Impeller Diameter
- 52 mm
- Impeller Width
- 19 mm
- Keyway
- Yes
- Housing Material
- Marine Grade Metals
- Manufacturing Standards
- ISO9002 Certified Factory (Aftermarket)
- Warranty
- 1 Year (Aftermarket)
What’s in the Box
- 1 x Impeller (6H4-44352-02-00)
- 1 x Pump Housing Cover (63D-44312-00-00)
- 1 x Cartridge Insert (63D-44322-00-00)
- 1 x Cartridge Outer Plate (66T-44323-00-00)
- 1 x Water Pump Gasket (63D-44316-00-00)
- 1 x Water Seal Damper (663-44366-00-00)
- 1 x O-Ring (93210-59MG7-00)
- 1 x Woodruff Key (90280-03M03-00)
- 4 x Bolts with Washer (90119-08M15-00)
Installation Notes
- Disconnect the battery and remove the engine cover. Locate and remove the bolts securing the lower unit (gearcase).
- Carefully separate the lower unit from the upper casing. Be mindful of the shift shaft linkage, which may need to be disconnected.
- Unbolt and remove the old water pump housing to access the impeller. Note the orientation of the old parts.
- Clean the mounting surfaces, driveshaft, and housing interior, removing any old gasket material or debris.
- Install the new key, gasket, wear plate, and impeller onto the driveshaft. Lubricate the new impeller and inside of the housing with a marine-safe grease.
- Install the new housing, insert, and seals, ensuring the impeller vanes are oriented correctly (curved in the direction of shaft rotation).
- Torque all bolts to the manufacturer's specified values.
- Re-assemble the lower unit to the engine, reconnect the shift shaft, and secure all mounting bolts.
- Once assembled, test the engine in water to confirm a strong and steady water stream from the tell-tale outlet.
Troubleshooting & FAQ
How do I know if this kit fits my engine?
The surest way is to match your engine's model number and year against our compatibility chart. If your model is listed, the kit is a confirmed fit. Also, cross-reference your existing part number with those in our Part Number Matrix.
What are the signs of a failing water pump impeller?
Common symptoms include the engine overheating at idle or low speeds, a weak or non-existent water stream from the "tell-tale" outlet, or a brittle or cracked appearance on the old impeller upon inspection.
How often should I replace the impeller?
As a preventative maintenance item, it is recommended to replace your water pump impeller every 100-200 operating hours or at least once a year, regardless of hours used. This is especially important if you operate in saltwater or sandy/silty conditions.
Does this kit fit any 2-stroke models?
Yes, while primarily for 4-stroke engines, this kit is also compatible with select Yamaha 40 HP 2-stroke models manufactured from 1998 onwards, including the 40X, 40XWT, and E40X series.
Is it necessary to replace the entire pump kit, or just the impeller?
For a reliable and long-lasting repair, it is highly recommended to replace the full kit, including the housing, wear plate, and gaskets. These components wear together over time, and a worn housing can cause a new impeller to fail prematurely.
What's the difference between OEM and this aftermarket kit?
This listing is an aftermarket replacement, not an OEM part. It has been engineered to meet or exceed original equipment specifications for fit, form, and function, using comparable high-quality materials. It is manufactured in an ISO 9002 certified facility and batch-inspected for quality assurance.
How fast do you ship and what are the costs?
We ship worldwide quickly—typical transit time is 5–15 days for most regions. Standard shipping is free on all orders. Expedited shipping options, if available for your location, will be presented at checkout.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal marine use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window provided the item is unused and in its original packaging. Please see our full policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchase. Even if your model is listed, variations can exist. Do not install if any differences are noted.
- This is an aftermarket replacement component, not an Original Equipment Manufacturer (OEM) product.
- Professional installation by a qualified marine mechanic is recommended to ensure safety and proper performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world reliability.
- Fast Global Fulfillment — We offer free standard delivery to most regions, with typical transit times of just 5–15 days.
- Manufacturer-Direct Value — By working directly with factories, we provide fair pricing without compromising on materials or quality control.
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