Water Pump Repair Kit – Fits Mercury/Mariner 25–50HP (Replaces 821354A2)

Water Pump Repair Kit – Fits Mercury/Mariner 25–50HP (Replaces 821354A2)

This water pump repair kit is designed for Mercury/Mariner 25–50HP 2-Stroke and 4-Stroke outboard engines. It provides the essential components needed to restore the performance and reliability of your engine's cooling system.

This kit is a direct replacement for Mercury/Mariner part numbers 821354A2 and 821354A1, as well as aftermarket parts from Sierra (18-4531), GLM (12045), and SEI (3219).

• Installation: Designed for a direct fit, replacing the original OEM components without modification.
• Complete Kit: Includes a new impeller, drive key, face plate, gaskets, and seals for a comprehensive service.
• Engine Health: Restores proper cooling system function to prevent overheating and potential engine damage.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Water Pump Impeller
• 1 x Drive Key
• 1 x Face Plate
• 1 x Upper Gasket (Replaces OEM 27-822189)
• 1 x Lower Gasket (Replaces OEM 27-822217)
• 2 x Washer (Replaces OEM 12-866451)
• 1 x Water Tube Seal

Installation Guide

1. Disconnect the battery and shift linkage before beginning.
2. Remove the lower unit mounting bolts and carefully lower the gearcase from the engine.
3. Unbolt and remove the old water pump housing to access the impeller.
4. Remove the old impeller, gaskets, and wear plate, noting the original orientation of the impeller vanes.
5. Thoroughly clean all mounting surfaces of any old gasket material or debris.
6. Install the new lower gasket, wear plate, and drive key onto the driveshaft.
7. Slide the new impeller onto the driveshaft, turning the shaft clockwise to bed the vanes correctly inside the housing.
8. Install the new upper gasket and secure the pump housing, torquing bolts to manufacturer specifications.
9. Apply a suitable sealant to the new water tube seal and install it.
10. Carefully reinstall the lower unit, ensuring the water tube, driveshaft, and shift shaft are correctly aligned.
11. Reconnect the shift linkage and battery connections.
12. Crucially, test the engine using a water supply (flushing attachment or in water) to verify proper water flow from the telltale outlet.

Troubleshooting & FAQ

Q: How do I know if this water pump kit will fit my Mercury engine?

A: This kit fits most Mercury/Mariner outboards in the 25-50HP range. The most reliable way to confirm fitment is to match your engine's serial number to the ranges listed in the "Compatible Engine Models" table above. If your model and serial number are listed, the kit will fit.

Q: What are the common signs that my water pump needs to be replaced?

A: Key symptoms include the engine overheating (especially at idle or low speeds), a weak or non-existent water stream from the "telltale" outlet, or finding brittle, cracked, or deformed impeller vanes during an inspection.

Q: How often should I replace my water pump impeller?

A: For preventative maintenance, we recommend replacing the water pump impeller and gaskets every 1-2 years or every 100-200 hours of use. Service intervals should be shorter if operating frequently in saltwater or silty/sandy conditions.

Q: OEM vs. Aftermarket?

A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?

A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?

A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.