Water Pump Impeller Repair Kit for Mercury/Mariner 25–50 HP – Replaces 821354A2
Water Pump Impeller Repair Kit for Mercury/Mariner 25–50 HP – Replaces 821354A2 is backordered and will ship as soon as it is back in stock.
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Water Pump Impeller Repair Kit for Mercury/Mariner 25–50 HP – Repla...
Water Pump Impeller Repair Kit for Mercury/Mariner 25–50 HP – Replaces 821354A2 is backordered and will ship as soon as it is back in stock.
Product Details
This water pump impeller repair kit is designed for selected Mercury and Mariner outboard applications in the 25–50 HP range. It replaces Mercury OEM water pump repair kit reference 821354A2 and is supplied without the water pump housing.
The kit renews the impeller and related water-pump service parts so an existing, serviceable housing can be rebuilt. Always confirm the engine model, stroke, gearcase configuration, and serial number before ordering.
- Aftermarket water pump repair kit for selected Mercury/Mariner outboards.
- Replaces Mercury OEM reference 821354A2.
- Includes an impeller, drive key, wear plate, gaskets, washers, and water tube seal.
- Housing is not included; reuse the existing housing only if it is undamaged and within service limits.
Part Number References
The following references are provided for identification and cross-reference purposes. Part-number references do not replace engine-specific fitment verification.
| Brand or Source | Reference | Application |
|---|---|---|
| Mercury | 821354A2 | OEM water pump repair kit reference |
| Sierra | 18-4531 | Water pump repair kit reference |
| GLM | 12045 | Impeller service kit reference; verify component and application details before substitution |
Engine & Model Compatibility
This kit is associated with selected Mercury and Mariner 25–50 HP applications using the 821354A2 water-pump configuration. Fitment varies by model, stroke, gear ratio, gearcase design, and serial-number range.
| Brand | Model or Rating | Stroke / Configuration | Reference | Serial or Application Notes |
|---|---|---|---|---|
| Mercury / Mariner | 25–50 HP | Selected 2-stroke and 4-stroke applications | 821354A2 | Verify the exact engine model and serial number before purchase. |
| Mercury | 30 HP, 2-cylinder | Gear housing/driveshaft applications | 821354A2 | Catalog records include multiple serial ranges, including 0G055314–0G760299, 0G760300–0T979999, 0T980000–0T999999, 1B000001 and up, 9854537–0P016999, 0P017000–0P325499, and 0P325500 and up. |
| Mercury | 30 HP Jet, 3-cylinder | Jet gearcase applications | 821354A2 | Applications include separate serial ranges and gear ratios; confirm the complete serial range and gearcase configuration. |
| Mercury | 40 HP, 2- or 3-cylinder and Jet applications | Selected gear housing/driveshaft applications | 821354A2 | Multiple serial ranges are cataloged; verify the exact model before ordering. |
Important: The horsepower range alone is not sufficient to confirm fitment. Compare the existing water-pump parts and check the engine serial number against the applicable Mercury/Mariner parts catalog.
Technical Specifications
- Product Type
- Water pump impeller repair kit
- Application
- Selected Mercury/Mariner 25–50 HP outboards
- Replacement Reference
- Mercury 821354A2
- Housing
- Not included
- Installation
- Service replacement for an existing compatible water pump assembly
- Brand Status
- Aftermarket replacement; not an OEM Mercury component
What’s in the Box
- 1 × Water pump impeller
- 1 × Drive key
- 1 × Wear or face plate
- 1 × Upper water pump gasket, reference 27-822189
- 1 × Lower water pump gasket, reference 27-822217
- 2 × Washer, reference 12-866451
- 1 × Water tube seal
The water pump housing, lower unit, driveshaft, fasteners, and lubricants are not included unless specifically listed above.
Installation Notes
- Disconnect the battery and follow the service manual for your specific engine.
- Support the outboard securely and remove the lower unit according to the manufacturer’s procedure.
- Remove the water pump housing and note the impeller-vane direction before disassembly.
- Remove the old impeller, key, gaskets, washers, wear plate, and water tube seal.
- Clean the mating surfaces and inspect the housing, wear plate, driveshaft, keyway, and water tube for damage or excessive wear.
- Install the new gasket, wear plate, drive key, impeller, remaining gasket, washers, and water tube seal in the same locations as the original parts.
- Use a suitable water-based lubricant or mild soapy water during impeller installation. Do not use petroleum-based grease on the rubber impeller.
- Reinstall the pump housing while rotating the driveshaft in the correct direction to seat the vanes.
- Reinstall the lower unit and tighten all fasteners to the engine manufacturer’s specified torque.
- Run the engine only in water or with an appropriate flushing device, and confirm a steady cooling-water tell-tale stream before normal operation.
Maintenance & Troubleshooting
How do I confirm that this kit fits my engine?
Match the engine brand, model, horsepower, stroke, gearcase configuration, and serial number with a parts catalog. The presence of 821354A2 on the old repair kit or parts diagram is the strongest identification clue. Do not rely on horsepower alone.
What are common signs of a worn water pump impeller?
Possible signs include a weak or intermittent tell-tale stream, overheating warnings, steam, or an impeller that is cracked, brittle, distorted, or missing vanes. Inspect the complete pump assembly when replacing the impeller.
Does the kit include the water pump housing?
No. This is a repair kit without the housing. It is intended for installation in an existing compatible housing that is not damaged or excessively worn.
Does it include the drive key and water tube seal?
Yes. The listed package contents include one drive key and one water tube seal, in addition to the impeller, wear plate, gaskets, and two washers.
How often should the impeller be replaced?
Inspect the impeller at the interval specified in the engine service manual and replace it whenever it shows wear, hardening, cracking, deformation, or damaged vanes. Service intervals may need to be shorter in saltwater, sandy, or silty operating conditions.
What if my serial number is not listed?
Do not assume fitment. Use the full engine serial number and compare the pump assembly with the applicable parts diagram before ordering.
Safety & Important Information
- Read and follow the engine manufacturer’s service instructions.
- Disconnect the battery before beginning work and support the lower unit safely.
- Do not operate the engine without an adequate water supply.
- Verify the parts, dimensions, and package contents against the original assembly before installation.
- This is an aftermarket replacement kit and is not manufactured by Mercury Marine.
About Sea Sierra
- Marine Replacement Parts — Practical aftermarket components for routine outboard service and repair.
- Application-Focused Information — Fitment references are provided to help customers compare engine and part-number details.
- Service Support — Confirm model and serial-number information before installation for the best fit.
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