Yanmar Seawater Pump Impeller Kit 119578-42750

The Yanmar 119578-42750 Impeller Kit is a genuine-style seawater pump service kit for select Yanmar marine diesel engines, most commonly the 6LY3 series. It is used to service the raw-water pump impeller, helping maintain proper seawater flow through the cooling system and reducing the risk of overheating. The kit is commonly listed with the impeller, cover O-ring, and cover screws/pins needed for routine seawater pump service.

Key Features

• Seawater pump impeller service kit
• Genuine Yanmar part reference: 119578-42750
• Used for raw-water pump / seawater pump maintenance
• Helps restore cooling-water flow through the seawater pump
• Common kit contents include:
  • Impeller
  • Cover O-ring
  • Cover plate screws / pins, quantity 6
• Supporting component references include 119578-42560 cover O-ring and 119578-42570 cover pins / screws
• Replaces earlier Yanmar references including 119574-42552 in supported applications

Engine Compatibility

This impeller kit is most strongly associated with Yanmar 6LY3 marine diesel engines, including 6LY3-ETP, 6LY3-STC, 6LY3-STP, 6LY3-UTC, and 6LY3-UTP models. Some catalog references also list 24V variants of these 6LY3 engines. Additional cross-reference sources show broader 6LYA and 6LY2 family associations, but fitment should be confirmed by the exact seawater pump and engine serial number before ordering.

Serial Number Fitment Notice

Seawater pump impeller fitment depends on the exact Yanmar engine model, seawater pump assembly, pump cover style, and serial number range. Confirm compatibility using the engine serial number and current pump parts diagram before ordering. Some references specifically list this kit for 6LY3-ETP / 6LY3-STP / 6LY3-UTP, while another reference notes it is not suitable for 6LY440 or 6LY2A models, so pump-level verification is important.

When This Part Needs Replacement

Replace the impeller during scheduled seawater pump service, after overheating, after dry running, or when the impeller vanes are cracked, stiff, worn, missing, or permanently bent. A weak or damaged impeller can reduce cooling-water flow and may lead to engine overheating.

Installation Notes

Inspect the pump cover, O-ring groove, cover screws, cam, wear plate, pump body, and shaft condition while the pump is open. Lubricate the new impeller as specified, install it in the correct rotation, and confirm the cover O-ring is seated properly before tightening the cover hardware evenly. After startup, verify seawater discharge and check for leaks at the pump cover.

Alternate/Superseded Part Numbers

• 119578-42750
• Yanmar 119578-42750
• YM11957842750
• 119574-42552
• 119574-42550
• 119574-42550-01
• 119574-42551
• Related kit component: 119578-42560 cover O-ring
• Related kit component: 119578-42570 cover pins / screws, quantity 6

Parts Desk Insight

This kit is best matched by the seawater pump assembly, not just the engine family. The 6LY series has several closely related models, and cross-references are not always consistent, so confirming the pump diagram before ordering helps avoid the wrong impeller kit.

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