Description

The Sierra 18-3077 Water Pump Impeller Kit is a complete service kit designed to restore proper cooling system performance in MerCruiser and OMC marine engines. This kit includes a high-quality flexible impeller along with essential gaskets, O-rings, and seals needed to service the raw water pump.

The impeller is responsible for circulating cooling water through the engine. Over time, the rubber vanes can wear, harden, or break down, reducing water flow and increasing the risk of overheating. Replacing the impeller and sealing components ensures reliable cooling and helps protect your engine from damage.

Manufactured to meet or exceed OEM specifications, this kit delivers dependable performance in both freshwater and saltwater environments.

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Key Features

• Complete raw water pump impeller service kit
• Includes impeller, gasket, O-ring, and seals
• Restores proper cooling water circulation
• OEM-equivalent fit and performance
• Durable marine-grade rubber impeller
• Sierra limited lifetime warranty

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Engine Compatibility

MerCruiser Engines

• Alpha One (Gen I)
• MR drives
• Select MerCruiser sterndrive engines

OMC Sterndrives

• Stringer drives
• Select OMC applications

Designed for engines using compatible raw water pump assemblies

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Serial Number Fitment Notice

Fitment depends on:

• Drive type (Alpha / MR / OMC)
• Pump housing configuration
• Engine serial number

Always confirm using:

• Engine serial number
• OEM part number match (18-3077)

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When This Part Needs Replacement

Replace the impeller kit if you notice:

• Weak or no water flow
• Engine overheating
• Cracked, missing, or stiff impeller vanes
• Reduced cooling efficiency
• After seasonal storage

Recommended service interval: every 100 hours or annually

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Installation Notes

• Lubricate impeller before installation
• Install with correct vane rotation
• Replace all included seals and gaskets
• Inspect pump housing and wear plate
• Ensure proper key alignment on shaft

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Alternate / Superseded Part Numbers

OEM Cross References

• Mercury / MerCruiser: 47-89984T4, 47-89984T2
• OMC: 777128, 3854286

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Aftermarket Cross References

• Sierra: 18-3077
• Mallory: 9-45605
• GLM: 12024

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Shipping

Shipping: Ships same or next day for fast Canada wide shipping.

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Parts Desk Insight

On Alpha and older OMC drives, the impeller is the first thing to go when cooling issues start. Even if it still looks okay, the rubber can lose flexibility and reduce water flow under load.

Doing the full kit instead of just the impeller helps ensure proper sealing and longer-lasting performance