SouthMarine Water Pump Repair Kit for Mercury 25-50HP — 821354A1 Compatible Impeller & Housing

SouthMarine's Boat Engine 821354A1 Water Pump Repair Kit is a complete replacement pack designed to restore cooling performance on Mercury 25–50HP outboard engines.

If your Mercury outboard is showing signs of overheating or reduced cooling water flow, this comprehensive SouthMarine kit supplies the primary wear parts needed for a dependable water pump rebuild. It replaces OEM part numbers including 821354A1, 821354A2, 3219 and 18-4531 and bundles components like a neoprene impeller, housing assembly, seals, gaskets, washers, a wear plate, and a drive key so you can complete the job in one service session.

How will this kit restore my outboard's cooling system?

The kit contains the core components that wear during normal operation—impeller, housing, wear plate, and seals—so replacing them returns the pump to near-original geometry and sealing. That helps re-establish proper water flow and pressure through the engine's cooling passages.

• Includes neoprene impeller compatible with Mercury 25–50HP models.
• Upper housing assembly (821351A3) for a correct fit.
• Wear plate and drive key to restore pump tolerances and rotation.

Which specific parts are inside and which engine numbers does it match?

This SouthMarine repair kit is packaged with every part commonly replaced during a water pump service so you won’t need to source extras. It’s intended for 25HP, 30HP, 40HP, 45HP and 50HP Mercury outboards and replaces several related OEM part numbers.

• Neoprene impeller (89640 / 47-85089-10 / 47-85089-3)
• Upper housing assembly 821351A3, wear plate 12505 (821354-2), gaskets, seals, washers, drive key
• Replaces part numbers: 821354A1, 821354A2, 3219, 18-4531

What tools and steps do I need to install the kit?

Installation requires basic marine-engine tools and moderate mechanical skill: remove the lower unit, open the pump housing, and swap worn parts for the new components following torque and alignment recommendations. Replace gaskets and seals, align the drive key, then reassemble and test for proper water discharge.

• Tools: socket set, screwdrivers, pliers, gasket scraper, torque wrench.
• Steps: remove lower unit → extract impeller → inspect housing → install new parts → reassemble and run test.
• Recommendation: note engine serial number if uncertain about fitment.

How long can I expect parts to last and when should I replace them?

Wear varies with use, water conditions, and storage. As a best practice, inspect or replace the impeller and seals annually or every 100 hours of operation; gaskets and the wear plate should be inspected at the same intervals for scoring or deformation.

• Impeller: check yearly or every boating season.
• Seals and gaskets: replace if cracked, flattened, or leaking.
• Wear plate: replace when scored or warped to maintain pump efficiency.

Who is this for: The SouthMarine 821354A1 Water Pump Repair Kit is made for boat owners, weekend anglers, and marine technicians who maintain Mercury 25–50HP outboards. It’s ideal if you want a single, organized package with all common replacement parts to perform an on-boat pump rebuild and restore reliable cooling without sourcing multiple individual components. If you’re unsure about fitment, provide your engine serial number before purchase to confirm compatibility.