Water Pump Repair Kit – Fits Mercury/Mariner 25–50HP (Replaces 821354A2, 821354A1)
Water Pump Repair Kit – Fits Mercury/Mariner 25–50HP (Replaces 821354A2, 821354A1) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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Water Pump Repair Kit – Fits Mercury/Mariner 25–50HP (Replaces 8213...
Water Pump Repair Kit – Fits Mercury/Mariner 25–50HP (Replaces 821354A2, 821354A1) is backordered and will ship as soon as it is back in stock.
Product Details
This Water Pump Repair Kit for Mercury/Mariner 25–50HP (Replaces 821354A2) is designed for a wide range of 2-stroke and 4-stroke outboard engines. It provides the essential components needed to restore the engine's cooling system to optimal performance, preventing overheating and ensuring reliability on the water.
It serves as a direct replacement for Mercury/Mariner part numbers 821354A2 and 821354A1, and interchanges with Sierra 18-4531, GLM 12045, and SEI 3219.
- Engineered for direct OEM replacement installation.
- Includes all essential gaskets, seals, and a new impeller.
- Built with OEM-quality components for durability.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/Mariner | 821354A2 |
| Mercury/Mariner | 821354A1 |
| Sierra | 18-4531 |
| GLM | 12045 |
| SEI | 3219 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit fits a variety of Mercury and Mariner outboards. Please verify your engine's serial number against the notes provided, as fitment can be specific.
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Mercury/Mariner | 25HP | 25 | 2-Stroke | 821354A2 | |
| Mercury/Mariner | 25HP | 25 | 4-Stroke | 821354A2 | Serial numbers: 0G531301 and up |
| Mercury/Mariner | 30HP | 30 | 2-Stroke | 821354A2 | |
| Mercury/Mariner | 30HP | 30 | 4-Stroke | 821354A2 | Serial numbers: 0G053314 and up |
| Mercury/Mariner | 30HP Jet | 30 | 821354A2 | Serial numbers: 0G590000 to 0T408999, 9973100 to 0P153499 | |
| Mercury/Mariner | 40HP | 40 | 2-Stroke | 821354A2 | |
| Mercury/Mariner | 40HP | 40 | 4-Stroke | 821354A2 | Serial numbers: 0G531301 and up (2 cyl), 0G590000 and up (3 cyl) |
| Mercury/Mariner | 45HP | 45 | 821354A2 | ||
| Mercury/Mariner | 50HP | 50 | 2-Stroke | 821354A2 | |
| Mercury/Mariner | 50HP | 50 | 4-Stroke | 821354A2 | Serial numbers: 0G590000 and up (3 cyl) |
Technical Specs
- Product Type
- Water Pump Repair Kit
- Installation
- Direct OEM replacement
- Other Technical Attributes
- OEM-quality replacement parts
What’s in the Box
- 1 x Water Pump Impeller
- 1 x Drive Key
- 1 x Face Plate
- 1 x Upper Gasket (27-822189)
- 1 x Lower Gasket (27-822217)
- 2 x Washer (12-866451)
- 1 x Water Tube Seal
Installation Notes
- Disconnect the negative battery cable before beginning work.
- Place a drain pan under the lower unit and remove the gear lube drain/fill screws to empty the oil.
- Remove the bolts securing the lower unit (gearcase) to the engine's midsection and carefully lower it.
- Unscrew the water pump housing bolts and lift the housing off the driveshaft.
- Note the rotational direction of the old impeller vanes before removing the impeller, gaskets, and face plate.
- Thoroughly clean all mating surfaces, removing any old gasket material or debris.
- Install the new lower gasket, face plate, and drive key.
- Slide the new impeller onto the driveshaft while turning the shaft clockwise to correctly seat the vanes inside the housing.
- Install the new upper gasket and reinstall the water pump housing, tightening bolts to the manufacturer's specified torque.
- Reattach the lower unit to the engine and refill the gearcase with new marine gear lube.
- Reconnect the battery and start the engine in water, ensuring a steady stream of water exits the tell-tale port.
Troubleshooting & FAQ
How do I know if this kit fits my specific engine model?
This kit is designed for a range of Mercury/Mariner 25–50HP engines. The most reliable method for confirming fitment is to check the "Engine & Model Compatibility" table and match your engine's serial number to the ranges provided. If your model is listed but serial number is not, visually compare the parts in the photos to your existing parts before ordering.
What are the signs of a failing water pump?
Common signs include a weak, intermittent, or completely absent water stream from the engine's "tell-tale" outlet. Other indicators are engine overheating alarms, steam from the exhaust, or finding a brittle, cracked, or melted impeller during a routine inspection.
How often should the water pump impeller be replaced?
For preventative maintenance, it is highly recommended to inspect the impeller each season and replace the complete water pump repair kit every 2-3 years or 200-300 hours of operation, whichever occurs first. Service intervals should be shorter for boats operating in saltwater or sandy/silty conditions.
Does this kit include the plastic water pump housing?
No, this is a repair kit containing the internal wear parts (impeller, gaskets, plate, etc.). It is designed to be installed into your existing, undamaged water pump housing.
My engine's serial number isn't in the compatibility list. Will this part still fit?
The serial numbers listed represent confirmed applications. If your serial number does not appear or fall within the specified ranges, this kit may not be correct for your engine. We do not recommend purchasing if your serial number does not match.
Is any special grease needed for installation?
Applying a light coat of marine grease or a soap-and-water solution to the inside of the pump housing and to the impeller vanes can ease installation and provide initial lubrication. Do not use petroleum-based grease, as it can damage the impeller rubber over time.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
Payment & Security
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