Sierra Impeller Gasket 18-2566-9, Replaces 27-430472, for Mercruiser Alpha I Generation 2, Pack of 2

The Sierra 18-2566-9 is an impeller gasket for the Mercruiser Alpha I - Generation 2 stern drive water pump, sold as a package of 2 gaskets. This gasket seats between the water pump housing and the impeller cavity to maintain a proper seal as raw water is drawn through the pump, preventing leaks and air intrusion that can reduce cooling flow. Because the gasket is a wear item that compresses and can tear during service, it is routinely replaced any time the water pump is opened up, such as during an impeller replacement or a full water pump rebuild. Installing a fresh gasket rather than reusing the old one helps ensure the pump housing seats correctly and seals under pressure, which protects engine cooling performance. This part is packaged two to a unit, so a single purchase supplies enough gaskets for one full water pump service with a spare on hand, or for two separate service jobs. It is designed as a direct fit for the Mercruiser Alpha I - Generation 2 application and cross-references to OEM part number 27-430472 for buyers matching against an original Mercruiser part number.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-2566-9
• Package Quantity: 2 gaskets per package
• Weight: 0.02 pounds
• UPC: 808282163006
• Category: Mercruiser Cooling System
• Component Type: Impeller gasket / water pump gasket

Fitment

• Mercruiser Alpha I - Generation 2 stern drive water pump

Replaces (OEM)

• 27-430472

Frequently Asked Questions

What does the Sierra 18-2566-9 impeller gasket fit? It fits the Mercruiser Alpha I - Generation 2 stern drive water pump.

How many gaskets come in a package of 18-2566-9? The 18-2566-9 is sold as a package of 2 gaskets, enough for one full water pump service with a spare or two separate jobs.

Is 18-2566-9 equivalent to Mercruiser part 27-430472? Yes, Sierra 18-2566-9 cross-references directly to Mercruiser OEM part number 27-430472.

When should this impeller gasket be replaced? The gasket should be replaced any time the Alpha I - Generation 2 water pump is opened, such as during an impeller swap or a full water pump rebuild, since it compresses and can tear during service.

How much does the 18-2566-9 gasket package weigh? The Sierra 18-2566-9 impeller gasket package weighs 0.02 pounds.

Can the old gasket be reused instead of installing 18-2566-9? Reusing a worn gasket is not recommended, because a compressed or torn gasket will not seal the water pump housing properly; installing a fresh 18-2566-9 gasket ensures a proper seal.

What is the UPC for the Sierra 18-2566-9 gasket? The UPC for the Sierra 18-2566-9 impeller gasket package is 808282163006.

Does 18-2566-9 fit other Mercruiser Alpha drive generations? This gasket is specified for the Alpha I - Generation 2 water pump; other Alpha drive generations use different gasket part numbers.

Is the 18-2566-9 gasket genuine Sierra or aftermarket equivalent? The 18-2566-9 is a Sierra-branded part manufactured to fit the Mercruiser Alpha I - Generation 2 water pump as a cross-reference to OEM number 27-430472.

What category of part is 18-2566-9? 18-2566-9 is an impeller gasket within the Mercruiser cooling system parts group, used to seal the water pump during impeller service.