Sierra 18-3320 Water Pump Kit for MerCruiser MR/Alpha I, Serial 6854393 to 0D594568

The Sierra 18-3320 Water Pump Kit is a replacement cooling system water pump kit built for MerCruiser MR/Alpha I sterndrive units, covering serial numbers 6854393 through 0D594568. The kit is engineered to meet or exceed the quality of the original equipment pump it replaces, giving boat owners a direct, fit-specific way to restore cooling system performance without sourcing individual components separately. Because MR/Alpha I lower units in this serial range share a common pump architecture, this kit is also the correct part for MerCruiser models that have been retro-fitted with an Alpha style lower unit lacking a pre-load pin in the top of the driveshaft, since those units must use Alpha style parts rather than the earlier housing-style components.

The kit is fit-specific to the listed serial number range, so boat owners should confirm their unit's serial number against the range before ordering to ensure proper fit. It is manufactured with glass-reinforced components for durability in the marine cooling environment and is sold under the Sierra brand as part number 18-3320.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3320
• Product Type: Water Pump Kit
• Material: Glass
• Weight: 0.98 pounds
• UPC: 030999315823
• Fitment: MerCruiser MR/Alpha I, serial numbers 6854393 to 0D594568
• Interchange Numbers: GLM 12120, Mallory 9-48307

Fitment

• MerCruiser MR/Alpha I sterndrive units, serial numbers 6854393 to 0D594568
• MerCruiser units retro-fitted with an Alpha style lower unit (no pre-load pin in top of driveshaft) must use Alpha style parts, including the 18-3320 water pump kit

Replaces (OEM)

• GLM 12120
• Mallory 9-48307

Frequently Asked Questions

What does the Sierra 18-3320 Water Pump Kit fit? This kit fits MerCruiser MR/Alpha I sterndrive units with serial numbers between 6854393 and 0D594568, and is fit-specific so the serial number should be confirmed before ordering.

Is 18-3320 the correct pump for a MerCruiser unit retro-fitted with an Alpha style lower unit? Yes. MerCruiser units that have been retro-fitted with an Alpha style lower unit, meaning there is no pre-load pin in the top of the driveshaft, must use Alpha style parts, and the Sierra 18-3320 is one of the correct parts for that configuration.

What OEM or aftermarket numbers cross-reference to the Sierra 18-3320? The Sierra 18-3320 Water Pump Kit is interchangeable with GLM 12120 and Mallory 9-48307.

How much does the 18-3320 water pump kit weigh? The Sierra 18-3320 Water Pump Kit weighs 0.98 pounds.

What material is the Sierra 18-3320 water pump kit made from? The kit uses glass-reinforced material in its construction, per the Sierra 18-3320 product specifications.

Will this water pump kit fit a MerCruiser with an older or newer serial number range than listed? No. The 18-3320 is fit-specific to MerCruiser MR/Alpha I units in the serial range 6854393 to 0D594568; units outside that range require a different Sierra water pump part number.

Does the Sierra 18-3320 meet original equipment quality standards? The kit is built to meet or exceed the quality of the original MerCruiser water pump component it replaces.

Is the 18-3320 a complete water pump kit or individual parts? The Sierra 18-3320 is sold as a complete Water Pump Kit rather than a single individual component.

How can I be sure I am ordering the right water pump for my MerCruiser MR/Alpha I unit? Check your MerCruiser drive unit's serial number against the range of 6854393 to 0D594568; the Sierra 18-3320 is fit-specific to that range, so matching the serial number is the way to confirm proper fit.

Is Mallory 9-48307 the same as the Sierra 18-3320? Mallory 9-48307 is a cross-referenced equivalent to the Sierra 18-3320 Water Pump Kit, along with GLM 12120.

What brand manufactures the 18-3320 water pump kit? The 18-3320 Water Pump Kit is manufactured under the Sierra brand.