Sierra 18-3412 Water Pump Kit with Housing – Yamaha 9.9 & 15 HP Outboard

Sierra 18-3412 is a complete water pump kit with housing for selected Yamaha 9.9 and 15 HP outboards. It supplies everything needed to fully service the lower-unit cooling water pump — including the impeller, housing, insert cup, wear plate, key, mounting bolts, and water-seal damper — making it the right choice when the existing housing, cup, or wear surfaces are scored, cracked, or worn beyond serviceability. If the housing is still in good condition, the related Sierra 18-3433 repair kit (without housing) may be sufficient.

Yamaha recommends water pump service every 100 hours or annually. Proactive impeller replacement prevents the leading cause of outboard overheating — a collapsed, cracked, or worn impeller that can no longer move adequate water volume through the cooling system.

Fitment note: Several different water pump kits are used across the Yamaha 9.9–15 HP family depending on model designation and production year. Confirm your exact Yamaha model, HP designation, and year before ordering. This kit replaces Yamaha OEM numbers 63V-W0078-01-00 and 63V-44301-00-00 on applicable engines.

Compatible Applications

• Yamaha 9.9 HP — 1996–2009
• Yamaha 15 HP — 1996–2009
• Yamaha F9.9 — 2005–2006
• Yamaha F15 — 1998–2005
• Yamaha T9.9 — 2005–2006
• Replaces Yamaha OEM: 63V-W0078-01-00 and 63V-44301-00-00
• Confirm engine model, HP designation, and year before ordering — multiple water pump kits are used across this engine family

Part Information

• Sierra part number: 18-3412
• SKU: 47-3412
• Brand: Sierra International
• Type: Complete water pump kit with housing
• Application: Yamaha 9.9 & 15 HP outboard lower-unit cooling water pump
• Replaces Yamaha: 63V-W0078-01-00, 63V-44301-00-00
• Related kit (without housing): Sierra 18-3433
• UPC: 808282287023
• Condition: New

Kit Contents

• Impeller — Sierra 18-3040
• Insert cup — Sierra 18-3444
• Impeller plate (wear plate) — Sierra 18-3195
• Mounting bolts — Sierra 18-0256 × 4
• Impeller key — Sierra 18-3294
• Water pump housing — Sierra 18-3356
• Water-seal damper — Sierra 18-1833

System Notes

• This kit services the lower-unit cooling water pump — the impeller draws water up through the gear case and into the engine cooling passages via the water tube
• Use the housing kit (18-3412) when the housing, insert cup, or wear plate shows scoring, cracking, or erosion — a worn housing will not seal correctly with a new impeller
• Use the Sierra 18-3433 repair kit (without housing) when the housing is still in serviceable condition
• A weakened tell-tale stream, intermittent water flow, or engine overheating warning are all indicators that the water pump needs service

Service Interval

• Yamaha recommends water pump service every 100 hours or annually, whichever comes first
• Replace the impeller any time the lower unit is removed for other service — the additional cost is minimal compared to a cooling failure
• Always inspect the housing, insert cup, and wear plate when replacing the impeller — worn surfaces reduce the effectiveness of a new impeller immediately
• Never re-use a removed impeller — impeller blades set a memory curve after running and will not pump as effectively once removed

Installation Notes

• Remove the lower unit and inspect the driveshaft, pump base, water tube, water tube seal, and all mating surfaces before assembly
• Clean all sealing surfaces — scoring on the wear plate or insert cup will allow water to bypass the impeller blades
• Lubricate the new impeller with a small amount of clean water or Yamaha water resistant grease before installing into the housing — do not use petroleum-based grease on the impeller
• Confirm the impeller key is correctly seated in the driveshaft keyway before pressing the housing down
• Rotate the driveshaft in the correct direction (clockwise when viewed from above) while pressing the housing over the impeller — this bends the impeller blades in the correct running direction
• Refer to the Yamaha service manual for your specific model for torque specifications and reassembly sequence

Technical FAQ

Q: How do I know if I need the full housing kit (18-3412) vs. just the repair kit (18-3433)?
Inspect the housing, insert cup, and wear plate after removing the lower unit. If any of these show scoring, cracking, or wear grooves from the impeller blades, the full kit (18-3412) is the right choice — a new impeller running against worn surfaces won’t pump as effectively and will wear faster. If all three components are smooth and undamaged, the 18-3433 repair kit is sufficient.

Q: How often should the water pump be serviced on my Yamaha 9.9 or 15 HP?
Every 100 hours or annually — whichever comes first. Many technicians recommend replacing the impeller any time the lower unit comes off for any reason, since the incremental cost of a new impeller is small compared to the cost of a cooling failure caused by a compromised impeller.

Q: Can I reuse the old impeller if it looks okay?
No. Impeller blades develop a running set (memory curve) during use. Even if the blades look intact, they will not pump as effectively once they have been removed and re-installed. Always fit a new impeller when servicing the water pump.

Q: My engine is overheating but the tell-tale is flowing — is the water pump still the issue?
Possibly. A worn impeller may still push enough water to produce a tell-tale stream but not enough volume to cool the engine adequately under load. Weak or intermittent tell-tale output at operating RPM is the clearest indicator. Also check the thermostat, water tube seal, and cooling passages for blockage before condemning the water pump alone.

Q: Does this kit fit the Yamaha 9.9 HP F9.9 and T9.9 models?
Yes — Sierra lists 18-3412 for the F9.9 (2005–2006) and T9.9 (2005–2006) in addition to the standard 9.9 HP and 15 HP models from 1996–2009. Confirm your exact model designation and year against the compatibility list above before ordering.

Related Yamaha Water Pump & Cooling Products

• Sierra 18-3433 Yamaha Water Pump Repair Kit — repair kit without housing; use when housing is still serviceable
• Sierra Water Pump Kit with Housing – Yamaha Outboard | SKU 47-35231 — related housing kit for other Yamaha models
• Sierra 3070 Yamaha Impeller
• Sierra 3071 Yamaha Impeller
• Sierra 3042 Yamaha Impeller
• Quicksilver 8M6012797 Water Pump Kit – Yamaha 60–70 HP
• Quicksilver 8M6012800 Impeller Repair Kit – Yamaha F70
• Quicksilver 8M6012801 Water Pump Kit – Yamaha F75–F100

Parts Desk Insights

The best use case for the 18-3412 is a water pump service where you know the housing needs to come out — either because inspection shows scoring or wear on the housing and cup, or because it’s a high-hour engine where you want to replace everything at once and not open the lower unit again for another service cycle. The key distinction from the 18-3433 is the housing — if the housing, insert cup, and wear plate are all in good shape, the 18-3433 saves money; if any of those three show wear, the 18-3412 is the right call. The most common issue we see is customers installing a new impeller without inspecting the housing surfaces — a new impeller running against a scored housing will wear prematurely and the pump will underperform from day one. The other common install issue is impeller blade direction — always rotate the driveshaft clockwise (when viewed from above) while pressing the housing down to ensure the blades are bent in the correct running direction.