Sierra 18-3320 Water Pump Repair Kit | MerCruiser MR & Alpha I
Sierra 18-3320 Water Pump Repair Kit | MerCruiser MR & Alpha I
Sierra
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Sierra 18-3320 — Water Pump Repair Kit | MerCruiser MR & Alpha I Sterndrives | S/N 6854393–0D469858
Sierra 18-3320 is a water pump repair kit with base and housing for MerCruiser MR and Alpha I stern drives from serial number 6854393 to 0D469858. Replaces MerCruiser 46-57234A8 and Mallory 9-48307. A reliable Sierra replacement that restores proper raw water flow through the sterndrive cooling system.
Part Specifications
- Sierra Part Number: 18-3320
- Type: Water pump repair kit with base and housing
- Application: MerCruiser MR and Alpha I stern drives
- Serial Number Range: 6854393–0D469858
- Kit Contents: Water pump housing and base
- Replaces MerCruiser: 46-57234A8
- Replaces Mallory: 9-48307
- Vendor: Sierra International
Confirm Fitment Before Ordering
Not sure if this kit fits your sterndrive? Give us your MerCruiser sterndrive model and serial number and we’ll confirm it for you before you order — by email, text, or live chat. Serial number range for this kit is 6854393–0D469858.
Additional Information
- Vendor: Sierra International
- Part Number: 18-3320
- OEM Cross-Reference: Replaces MerCruiser 46-57234A8; Mallory 9-48307
- Application: MerCruiser MR and Alpha I sterndrives, S/N 6854393–0D469858
- Kit Contents: Water pump housing and base
Installation Notes
Install following the applicable MerCruiser service manual for your MR or Alpha I sterndrive model. Confirm your sterndrive serial number falls within range 6854393–0D469858 before beginning installation.
Frequently Asked Questions
Q: What MerCruiser sterndrives does Sierra 18-3320 fit?
A: Sierra 18-3320 fits MerCruiser MR and Alpha I stern drives with serial numbers from 6854393 to 0D469858. Not sure if this fits your sterndrive? Give us your sterndrive model and serial number and we’ll confirm it — by email, text, or live chat.
Q: What OEM part numbers does Sierra 18-3320 replace?
A: Sierra 18-3320 replaces MerCruiser 46-57234A8 and Mallory 9-48307. If your service manual or existing parts reference either of these numbers, 18-3320 is the Sierra replacement.
Q: What is included in the kit?
A: The Sierra 18-3320 kit includes the water pump housing and base. Confirm whether your installation requires additional components such as an impeller, seal, or hardware before ordering.
Q: What is the difference between the MR and Alpha I drives?
A: The MR (Mercury Racing) drive preceded the Alpha I in MerCruiser’s sterndrive lineup. The Alpha I replaced the MR drive and shares many service components in the overlapping serial number range. Confirm your specific drive model using your serial number and the MerCruiser parts catalog before ordering.
Q: How often should the water pump be serviced on a MerCruiser sterndrive?
A: MerCruiser recommends water pump inspection and impeller replacement at regular service intervals — typically every 2–3 years or 200–300 hours, whichever comes first. Refer to your MerCruiser service manual for the interval specific to your drive model.
! Compatibility references are provided for informational purposes only and do not constitute a fitment guarantee. Part numbers, application listings, and "replaces" cross-references are based on manufacturer data and are intended as a starting point for identification — not a guarantee of fit for your specific engine, hull, or installation.
Buyer is solely responsible for verifying compatibility with their engine model, serial number, model year, and trim configuration before purchase. If you are unsure whether this part fits your application, contact MacombMarineParts.com before you buy — we're available via text, email, or online chat to help verify compatibility for your specific application.
MacombMarineParts.com is not liable for parts ordered based on assumed fitment. Returns due to buyer-selected incorrect fitment are subject to our standard return and restocking fee policies.