Water Pump Repair Kit Without Housing for Mercury/Mariner 25–50 HP Outboards – Replaces 821354A2
Water Pump Repair Kit Without Housing for Mercury/Mariner 25–50 HP Outboards – Replaces 821354A2 is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Water Pump Repair Kit Without Housing for Mercury/Mariner 25–50 HP ...
Water Pump Repair Kit Without Housing for Mercury/Mariner 25–50 HP Outboards – Replaces 821354A2 is backordered and will ship as soon as it is back in stock.
Product Details
This water pump repair kit without housing is designed for specified Mercury and Mariner outboards using the water pump assembly associated with Mercury OEM part number 821354A2. It is an aftermarket replacement intended to renew the pump's impeller, wear plate, gaskets, seals, and washers while reusing the existing water pump housing when it remains serviceable.
The kit corresponds to Sierra 18-4531 and replaces Mercury 821354A2. The catalog application list covers the following Mercury/Mariner configurations: 25 HP 4-stroke, 30 HP 2-cylinder 2-stroke, 30 HP 4-stroke, 40 HP 2-cylinder 2-stroke, 40 HP 3-cylinder 2-stroke, 40 HP 4-stroke, 50 HP 3-cylinder 2-stroke, 50 HP 4-stroke, and 50 Bigfoot 4-stroke models.
- Repair-kit format without a water pump housing.
- Includes the primary wear and sealing components for a standard water pump service.
- Use with the original housing only after checking it for cracks, corrosion, scoring, and excessive wear.
Part Number Matrix
Use the following documented references to compare the kit with the part identified for your engine.
| Brand | Part Number | Reference Type |
|---|---|---|
| Mercury | 821354A2 | OEM replacement reference |
| Sierra | 18-4531 | Aftermarket water pump repair kit without housing |
Engine & Model Compatibility
Confirm the complete engine configuration, including horsepower, cylinder arrangement, stroke, model designation, and serial-number range where applicable. The applications below are grouped by configuration; they do not confirm every year or serial number within a horsepower family.
| Brand | Model / Configuration | Rated HP | Stroke | OEM Reference |
|---|---|---|---|---|
| Mercury/Mariner | 25 | 25 | 4-Stroke | 821354A2 |
| Mercury/Mariner | 30, 2-cylinder | 30 | 2-Stroke | 821354A2 |
| Mercury/Mariner | 30 | 30 | 4-Stroke | 821354A2 |
| Mercury/Mariner | 40, 2-cylinder | 40 | 2-Stroke | 821354A2 |
| Mercury/Mariner | 40, 3-cylinder | 40 | 2-Stroke | 821354A2 |
| Mercury/Mariner | 40 | 40 | 4-Stroke | 821354A2 |
| Mercury/Mariner | 50, 3-cylinder | 50 | 2-Stroke | 821354A2 |
| Mercury/Mariner | 50 | 50 | 4-Stroke | 821354A2 |
| Mercury/Mariner | 50 Bigfoot | 50 | 4-Stroke | 821354A2 |
Technical Specs
- Product Type
- Water pump repair kit without housing
- Installation
- Aftermarket replacement for the specified water pump assembly
- Housing Included
- No; reuse the original housing only if it is in serviceable condition
- Impeller Material
- Neoprene rubber
- Wear Plate
- Replacement wear plate included
- Dimensions
- 152.4 × 114.3 × 38.1 mm (6 × 4.5 × 1.5 in), packaging dimensions
- Weight
- 0.18 kg (5.3 oz)
- Warranty
- 1 year
What’s in the Box
This kit is supplied without the water pump housing and does not include an impeller key.
- 1 × Water pump impeller — aftermarket replacement for Mercury 47-85089-series impeller references
- 1 × Wear plate — aftermarket replacement for Mercury 8213542
- 1 × Upper water pump gasket — aftermarket replacement for Mercury 27-822189
- 1 × Lower water pump gasket — aftermarket replacement for Mercury 27-822217
- 1 × Short tube seal — aftermarket replacement for Mercury 43023
- 1 × Long tube seal — aftermarket replacement for Mercury 823547-1
- 2 × Washer — aftermarket replacement for Mercury 12-86645-1
Installation Notes
- Disconnect the battery and remove the engine cover.
- Drain the gearcase lubricant from the lower unit.
- Remove the fasteners securing the lower unit to the engine midsection and carefully lower the unit.
- Locate the water pump on top of the gearcase and remove the pump-housing fasteners.
- Remove the old impeller, wear plate, gaskets, seals, and washers. Inspect the existing housing and clean all mating surfaces.
- Before installation, confirm that the original impeller key is present, undamaged, and suitable for reuse. This kit does not include a key.
- Install the new gaskets, wear plate, seals, washer set, and impeller. Orient the impeller vanes according to the engine service manual.
- Apply an appropriate water-pump lubricant or clean soapy water as recommended by the service manual, then reinstall the original housing.
- Tighten the pump and lower-unit fasteners to the manufacturer’s specified torque.
- Reinstall the lower unit, ensuring the water tube, shift shaft, and driveshaft align correctly. Refill the gearcase lubricant and test the engine with an adequate water supply.
Troubleshooting & FAQ
How do I know if my water pump needs service?
Common signs include a weak or intermittent tell-tale stream, an overheating alarm, excessive engine temperature, or steam from the exhaust. During inspection, replace an impeller that is stiff, cracked, deformed, or missing vanes, and inspect the wear plate and housing for scoring or corrosion.
Does this kit include the water pump housing?
No. This is a repair kit without housing. Inspect your original housing carefully and replace it separately if it is cracked, badly corroded, or worn beyond the service limits in the engine manual.
Does this kit include an impeller key?
No. The documented kit contents include the impeller, wear plate, gaskets, tube seals, and two washers, but no impeller key. Confirm that your existing key is present and reusable before beginning installation.
Will this kit fit my specific engine serial number?
Fitment depends on the complete configuration, not horsepower alone. Compare your engine’s model, year, stroke, cylinder arrangement, and serial-number range with the service information for your outboard, and verify that the existing pump assembly uses Mercury 821354A2.
How often should a water pump impeller be replaced?
Replacement intervals vary by manufacturer and operating conditions. Saltwater, sand, silt, long storage periods, and overheating can shorten impeller life. Follow the maintenance schedule in your engine service manual and inspect the pump whenever cooling performance declines.
Is this an OEM part?
No. This is an aftermarket replacement kit intended to replace the specified water pump service components. Mercury and Sierra numbers shown on this page are reference numbers only.
Shipping speed & cost
We ship worldwide quickly. Typical transit is 5–15 days. Standard shipping is free, and expedited options will appear at checkout where available.
Warranty & returns
This product is covered by a 1-year warranty against manufacturing defects under normal use. If an issue arises, contact our support team with your order details. Returns are accepted within the standard return window for unused items in their original condition.
Safety & Important Info
- Verify the complete engine application and compare the original water pump components before purchase.
- This kit does not include the water pump housing or impeller key.
- Do not operate the engine without an adequate cooling-water supply.
- Professional installation is recommended when lower-unit or cooling-system service is unfamiliar.
About Sea Sierra
- Pro-Grade Standards — We supply marine replacement parts engineered for demanding real-world conditions.
- Fast Global Fulfillment — We offer free standard delivery to most regions, with typical transit times of 5–15 days.
- Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing while maintaining consistent product quality.
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