Water Pump Impeller Kit for Select Yamaha 40/50 HP 2-Stroke Outboards – Replaces 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00, Sierra 18-3429 and 18-3408
Water Pump Impeller Kit for Select Yamaha 40/50 HP 2-Stroke Outboards – Replaces 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00, Sierra 18-3429 and 18-3408 is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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Water Pump Impeller Kit for Select Yamaha 40/50 HP 2-Stroke Outboar...
Water Pump Impeller Kit for Select Yamaha 40/50 HP 2-Stroke Outboards – Replaces 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00, Sierra 18-3429 and 18-3408 is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket water pump impeller kit is designed for select Yamaha 40 HP and 50 HP 2-stroke outboards. It is intended to replace the water pump service components identified by Yamaha part numbers 6H4-W0078-00-00, 6H4-W0078-01-00 and 6H4-W0078-A0-00, with aftermarket interchange references including Sierra 18-3429 and 18-3408.
The kit supplies the impeller, key, wear plate, insert cup, gaskets, grommet and mounting hardware required for a water pump service on compatible engines. Always compare the exact engine model, year and serial-number application with the original part before ordering.
- Application: Select Yamaha 40 HP and 50 HP gasoline 2-stroke outboards.
- Replacement type: Aftermarket replacement for the listed OEM and aftermarket references.
- Impeller: Neoprene rubber construction for marine cooling-system use.
- Service coverage: Components for servicing the water pump assembly; confirm the package contents below before installation.
Part Number Matrix
These are the customer-facing OEM and aftermarket reference numbers associated with this kit.
| Brand | Part Number |
|---|---|
| Yamaha | 6H4-W0078-00-00 |
| Yamaha | 6H4-W0078-01-00 |
| Yamaha | 6H4-W0078-A0-00 |
| Sierra | 18-3429 |
| Sierra | 18-3408 |
Engine & Model Compatibility
The following model and year applications are provided as a compatibility guide for the listed water-pump references. Model suffixes, shaft configurations and serial-number ranges can affect fitment. Confirm the exact model and serial number before purchase.
| Brand | Model | Rated HP | Stroke | Year | Reference | Application note |
|---|---|---|---|---|---|---|
| Yamaha | 40ELN, 40ESN, 40LN, 40SN | 40 | 2-Stroke | 1984 | 6H4-W0078-00-00 | Lower Drive 1 / repair kit application |
| Yamaha | 40ELK, 40ESK, 40ETLK, 40LK, 40SK | 40 | 2-Stroke | 1985 | 6H4-W0078-00-00 | Lower Drive 1 / repair kit application |
| Yamaha | 40ELJ, 40ESJ, 40ETLJ, 40LJ, 40SJ, 40SJ-JD | 40 | 2-Stroke | 1986 | 6H4-W0078-00-00 | Repair kit application |
| Yamaha | 40ELH, 40ESH, 40ETLH, 40LH, 40SH, 40SH-JD | 40 | 2-Stroke | 1987 | 6H4-W0078-00-00 | Repair kit application |
| Yamaha | 40ELG, 40ESG, 40ETLG, 40LG, 40SG, 40SG-JD | 40 | 2-Stroke | 1988 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | 40ELF, 40ESF, 40ETLF, 40LF, 40SF, 40SF-JD | 40 | 2-Stroke | 1989 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | 40ELD, 40ESD, 40ETLD, 40LD, 40SD, 40SD-JD | 40 | 2-Stroke | 1990 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | 40EJRP, 40ELRP, 40ESRP, 40MJHP, 40MLHP, 40MSHP, 40PLRP | 40 | 2-Stroke | 1991 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | 40 standard models | 40 | 2-Stroke | 1992–1994 | 6H4-W0078-00-00 | Confirm the exact model and serial number |
| Yamaha | 50ETLN, 50ETSN | 50 | 2-Stroke | 1984 | 6H4-W0078-00-00 | Lower Drive 1 / repair kit application |
| Yamaha | 50ETLK, 50ETSK | 50 | 2-Stroke | 1985 | 6H4-W0078-00-00 | Repair kit application |
| Yamaha | 50ELJ, 50ELJ-JD, 50ESJ, 50ETLJ | 50 | 2-Stroke | 1986 | 6H4-W0078-00-00 | Repair Kit 2 or repair kit application |
| Yamaha | 50ELH, 50ESH, 50ESH-JD, PRO50LH | 50 | 2-Stroke | 1987 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | 50ELG, 50ESG, 50ESG-JD, PRO50LG | 50 | 2-Stroke | 1988 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | 50ELF, 50ESF, 50ESF-JD, PR50LF, PRO50LF | 50 | 2-Stroke | 1989 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | 50ELD, 50ESD, 50ESD-JD, 50ETMLD, PRO50LD | 50 | 2-Stroke | 1990 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | 50EJRP, 50ELRP, 50ERP, 50TLHP, P50TLRP | 50 | 2-Stroke | 1991 | 6H4-W0078-00-00 | Repair Kit 2 application |
| Yamaha | P50 | 50 | 2-Stroke | 1995–1996 | 6H4-W0078-00-00 | Some later models may use 63D-W0078-01 |
Technical Specifications
- Product Type
- Water pump impeller kit
- Installation
- Replacement water-pump service kit; professional installation is recommended
- Engine Type
- Compatible gasoline marine outboards as listed above
- Housing Components
- Stainless-steel plates and plastic insert cup
- Impeller Material
- Neoprene rubber
- Package Dimensions
- 155 × 105 × 50 mm (6.1 × 4.13 × 1.97 inches)
- Weight
- 0.22 kg (7.7 oz)
- Marine Use
- Designed for water-pump service in marine environments
What’s in the Box
- 1 × Water pump impeller, Yamaha reference 6H4-44352-00
- 1 × Woodruff key, Yamaha reference 90280-03024
- 1 × Wear plate, Yamaha reference 663-44323-00
- 1 × Insert cup, Yamaha reference 663-44322-00
- 1 × Gasket, Yamaha reference 663-44315-A0
- 1 × Gasket, Yamaha reference 663-44316-A0
- 1 × Gasket, Yamaha reference 663-44324-A0
- 1 × Grommet, Yamaha reference 663-44366-00
- 2 × Bolt, Yamaha reference 97080-08045
- 2 × Bolt, Yamaha reference 97080-08055
Installation Notes
- Disconnect the negative battery cable and follow the engine manufacturer’s safety procedures.
- Drain the gearcase oil from the lower unit.
- Remove the mounting bolts and detach the lower unit from the engine.
- Remove the water-pump housing bolts and lift the housing off carefully. Note the direction of the original impeller vanes.
- Remove the old impeller, key, wear plate, insert cup and gaskets.
- Clean the housing and mating surfaces thoroughly, removing old gasket material and corrosion.
- Install the new wear plate, gaskets, insert cup and grommet from the kit.
- Fit the woodruff key into the driveshaft slot, install the impeller and rotate the driveshaft clockwise to set the vanes in the correct direction.
- Apply a light coat of suitable marine lubricant to the inside of the pump cup, reinstall the housing and tighten the bolts to the engine manufacturer’s specifications.
- Reinstall the lower unit, ensuring that the water tube and shift shaft are correctly aligned.
- Refill the gearcase with the specified marine gear oil.
- Reconnect the battery and test the engine using an appropriate flusher or while in the water. Confirm a steady tell-tale stream and monitor for overheating.
Troubleshooting & FAQ
How do I know if my water-pump impeller is failing?
Common signs include a weak or missing tell-tale stream, an overheating alarm or an unusually high engine temperature. Inspect the cooling system and replace the impeller at the interval recommended for your exact engine and operating conditions.
Will this kit fit a Yamaha 50 HP model made after 1996?
This application guide includes selected P50 models through 1996. Some later Yamaha 50 HP models may use a different water-pump reference, such as 63D-W0078-01. Confirm the exact model, year, serial number and OEM part number before ordering.
What is the woodruff key, and is it included?
The woodruff key locks the impeller to the driveshaft so that the impeller rotates with the shaft. One woodruff key, reference 90280-03024, is included in the kit.
Are the included gaskets and bolts sufficient for the listed service?
The kit includes the gaskets, wear plate, insert cup, grommet and bolts listed in the package-contents section. Compare the contents with the parts removed from your engine before beginning the repair.
Is this a genuine OEM part?
No. This is an aftermarket replacement kit that references the listed Yamaha and Sierra numbers for application identification. Yamaha and Sierra are trademarks of their respective owners.
How fast is shipping and what does it cost?
Shipping availability, delivery estimates and applicable charges are shown at checkout and may vary by destination and service level.
What is the warranty and return policy?
Warranty coverage and return eligibility are governed by the seller’s current policy. Contact customer support with your order details if you need assistance.
Safety & Important Information
- Verify the exact engine model, year and serial number before purchase.
- Compare the original water-pump components and OEM reference with the application information above.
- Do not operate an outboard with a suspected cooling-system failure or without an adequate water supply.
- This is an aftermarket replacement part, not a genuine OEM component.
- Professional installation is recommended, particularly when removing or reinstalling the lower unit.
About Sea Sierra
- Pro-Grade Standards — Marine replacement parts selected for dependable service in demanding marine environments.
- Global Fulfillment — Shipping options and delivery estimates are provided at checkout.
- Manufacturer-Direct Value — Competitive replacement-part pricing without representing aftermarket products as genuine OEM components.
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