Sierra 18-3321 Complete Water Pump Kit for Mercruiser Stern Drive, Serial 2495186-2763441

The Sierra 18-3321 is a complete water pump kit built for Mercruiser stern drive units, specifically the number 1 units with a plastic flush screw in the gear housing, covering serial number range 2495186 through 2763441. This kit replaces the entire water pump assembly rather than a single component, giving boat owners everything needed to restore full cooling system pumping capacity in one purchase. The kit is built from metal construction to withstand the marine environment and the heat and pressure cycles of an operating stern drive cooling circuit.

Because the water pump is one of the most common wear items on a stern drive, replacing the complete assembly at once helps ensure the housing, base, and impeller are matched and sealing correctly together, rather than mixing a new impeller with a worn housing or base. This kit is application-specific to the number 1 unit configuration with the plastic flush screw in the gear housing, so confirming the gear housing type and serial number before ordering is important, since Mercruiser used different pump configurations across different serial number ranges and drive types.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3321
• Product Type: Complete Water Pump Kit
• Application: Mercruiser stern drive, #1 Units with plastic flush screw in gear housing
• Serial Number Range: 2495186 - 2763441
• Material: Metal
• Weight: 0.98 pounds
• Unit Count: 1
• UPC: 030999315830
• GTIN: 00030999315830
• Related Sierra Component Numbers: Upper Pump Housing 18-3116, Upper Pump Kit 18-3517, Water Pump Base 18-3421, Impeller Repair Kit (no housing) 18-3217, Impeller 18-3017
• Warranty: Limited warranty

Fitment

• Mercruiser stern drive, #1 Units with plastic flush screw in gear housing, serial numbers 2495186 through 2763441

Frequently Asked Questions

What is included in the Sierra 18-3321 water pump kit? The Sierra 18-3321 is a complete water pump kit, meaning it includes the full pump assembly rather than a single part, for Mercruiser #1 units with a plastic flush screw in the gear housing.

Which Mercruiser units does the 18-3321 fit? It fits Mercruiser #1 units with a plastic flush screw in the gear housing, covering serial number range 2495186 through 2763441.

How do I know if my Mercruiser unit takes the 18-3321 instead of a different pump kit? Check the gear housing for a plastic flush screw and confirm your unit's serial number falls within 2495186 to 2763441; units in this range with the plastic flush screw take the 18-3321 complete kit.

What material is the Sierra 18-3321 water pump kit made from? The 18-3321 kit is made of metal, sized for the heat and pressure of a stern drive cooling circuit.

How much does the 18-3321 water pump kit weigh? The Sierra 18-3321 weighs 0.98 pounds.

What is the difference between the 18-3321 and the 18-3317 water pump kits? The 18-3321 is for #1 units with a plastic flush screw in the gear housing (serial numbers 2495186-2763441), while the 18-3317 is the equivalent complete kit for #1 units without a flush screw in the gear housing, covering serial numbers 2763442-6854392.

Will the 18-3321 fit an MR or Alpha I stern drive? No. MR/Alpha I units use a different complete water pump kit, part number 18-3320, so confirm your unit type before ordering the 18-3321.

Can I buy just the impeller instead of the full 18-3321 kit? Yes, the impeller used in this application is available separately as part number 18-3017, though the 18-3321 complete kit replaces the housing, base, and impeller together.

Is the housing included in the 18-3321, or just repair parts? The 18-3321 is a complete kit that includes the pump housing along with the pump base and impeller, not just a repair-only impeller kit.

Is the Sierra 18-3321 an OEM part or an aftermarket replacement? The 18-3321 is a Sierra-manufactured replacement kit engineered to meet or exceed the performance of the original equipment water pump it replaces.

What is the Sierra part number for the upper pump housing alone if I only need that piece? For #1 units with a plastic flush screw (the same application as the 18-3321), the upper pump housing is sold separately as part number 18-3116.

Does the 18-3321 come with a warranty? Yes, the Sierra 18-3321 water pump kit is covered under Sierra's limited warranty.