Water Pump Impeller Kit – Fits Mercury/Mariner 25-50 HP 4-Stroke (Replaces 821354A2)

$29.68 $47.00

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Water Pump Impeller Kit – Fits Mercury/Mariner 25-50 HP 4-Stroke (Replaces 821354A2) is backordered and will ship as soon as it is back in stock.

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Product Details

This Water Pump Impeller Kit – Fits Mercury/Mariner 25-50 HP 4-Stroke Outboards (Replaces 821354A2) provides the essential components to restore your engine's cooling system. It is designed for Mercury/Mariner 25-50 HP 4-Stroke outboard engines from 1998 and newer, and also fits select Force 40-50 HP models from 1995–1997.

This kit is a direct interchange for Mercury part numbers 821354A1, 821354A2, and 821354A04, as well as Sierra 18-4531, Quicksilver 821354A2, and GLM 12045.

Engineered for direct-fit installation in the lower unit water pump housing.
Features a durable neoprene rubber impeller and a stainless steel wear plate for longevity.
Includes all necessary gaskets, seals, and hardware for a complete service.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket brands.

Brand	Part Number	Notes
Mercury	821354A1	Superseded by 821354A2
Mercury	821354A2	Current OEM Number
Quicksilver	821354A2
Mercury	821354A04	Supersedes 821354A2
Sierra	18-4531	Aftermarket Equivalent
GLM	12045	Aftermarket Equivalent

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This kit fits a wide range of Mercury and Mariner outboards from 1998 to the present day, primarily in the 25-50 HP class. It also covers specific two-stroke Force models.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	25 HP Four Stroke Carb	25	4-Stroke	1998–Up	821354A2	0G590000-0T408999
Mercury	30 HP Four Stroke Carb	30	4-Stroke	1998–Up	821354A2	0G760300-0T408999
Mercury	30 HP Jet	30	4-Stroke	1998–Up	821354A2	0G590000-Up
Mercury	30/40 HP (2 Cyl)	30-40	2-Stroke	1998–Up	821354A2	0G053314-Up
Mercury	40 HP (3 Cyl)	40	2-Stroke	1998–Up	821354A2	0G531301-Up
Mercury	40/45 HP Four Stroke 2:1	40-45	4-Stroke	1998–Up	821354A2	0G760300-0T408999
Mercury	45 HP Four Stroke Bodensee	45	4-Stroke	1998–Up	821354A2	0G231123-Up
Mercury	50 HP (3 Cyl)	50	2-Stroke	1998–Up	821354A2	0G590000-Up
Mercury	50 HP Four Stroke	50	4-Stroke	1998–Up	821354A2	0G231123-Up
Mercury	50 HP BigFoot	50	4-Stroke	1998–Up	821354A2
Mariner	25-50 HP Models	25-50	4-Stroke	1998–Up	821354A2	Same applications as Mercury
Force	Outboard	40	2-Stroke	1995–1997	821354A2	Serial ranges: 0E093700-0E287999
Force	Outboard	50	2-Stroke	1995–1997	821354A2	Serial ranges: 0E093700-0E287999

Technical Specs

Product Type: Water Pump Impeller Kit
Installation: Engine Lower Unit
Connection: Direct Drive
Housing Material: Stainless Steel Wear Plate, Nylon PA66 Tube
Housing Color: Silver/Black
Weight: 0.15 kg (5.3 oz)
Fitting Type: Direct Fit to Water Pump Housing
Impeller Material: Neoprene Rubber

What’s in the Box

1 x Water Pump Impeller (47-85089/8508910/850893/8M0027792/8M0024502)
1 x Impeller Drive Key (85119)
1 x Wear Plate (8213542)
1 x Upper Gasket (27-822189)
1 x Lower Gasket (27-822217)
1 x Short Tube Seal (43023)
1 x Long Tube Seal (8235471/823547-1)
2 x Washer (12-86645)

Installation Notes

Disconnect the battery and remove the engine cowling. Shift the outboard into neutral.
Place a drain pan under the lower unit and remove the gearcase oil drain/fill screws to drain the oil.
Remove the bolts connecting the lower unit (gearcase) to the upper driveshaft housing. Carefully separate the lower unit.
Locate the water pump housing on top of the gearcase and remove its mounting bolts.
Slide the housing up and off the driveshaft to expose the impeller. Note the orientation of the impeller vanes.
Remove the old impeller, drive key, gaskets, and wear plate. Clean all mating surfaces thoroughly.
Install the new wear plate, gaskets, drive key, and impeller. Ensure the new impeller vanes are oriented correctly (typically bent counter-rotation).
Lubricate the inside of the housing and apply sealant to the gaskets if specified. Reinstall the housing.
Reattach the lower unit, ensuring the driveshaft, shift shaft, and water tube align correctly.
Refill the gearcase with fresh oil, reinstall the engine cowling, and reconnect the battery. Test run the engine using a water supply, checking for a strong tell-tale stream.

Troubleshooting & FAQ

How do I confirm this kit fits my specific engine model?

The surest way is to match your engine's model, horsepower, and year against our compatibility table. For Mercury/Mariner engines, the serial number range is critical for ensuring a perfect fit. Cross-reference the OEM part number (821354A2) with your engine's service manual if possible.

What are the signs of a failing water pump impeller?

Common symptoms include a weak or non-existent water stream from the "tell-tale" outlet, engine overheating alerts or alarms, and steam from the exhaust. Reduced engine performance at idle or high RPM can also indicate a cooling issue.

How often should I replace my outboard's impeller?

As a preventative maintenance item, most manufacturers recommend replacing the impeller every 100-200 operating hours or at least annually at the beginning of the boating season, whichever comes first. This helps prevent unexpected failures on the water.

What causes an impeller to fail prematurely?

The most common causes are running the engine dry (even for a few seconds), sucking up sand or silt in shallow water, and age-related hardening of the rubber. Regular inspection and replacement are key to avoiding these issues.

Is the small metal drive key important?

Yes, the drive key is critical. It locks the impeller to the driveshaft, forcing it to spin. If the key is lost or not installed, the driveshaft will spin freely inside the impeller, and the pump will not move any water, leading to immediate engine overheating.

What is the difference between this and an OEM part?

This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, our parts are batch-inspected for consistency and reliable performance.

How fast is shipping?

We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free for most regions. Expedited options, if available for your location, will appear at checkout.

What is your warranty and return policy?

This part is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window, provided the product is unused and in its original condition. See our policy page or reach out for instructions.

Safety & Important Info

Verify images and specifications against your original part before purchase. If anything differs—even if your model appears compatible—do not install the part.
This is an aftermarket replacement component, not an original equipment manufacturer (OEM) part.
Professional installation is highly recommended for safety and optimal performance. Improper installation can lead to engine damage.

About Sea Sierra

Pro-Grade Standards: We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world conditions.
Fast Global Fulfillment: We offer free standard delivery to most regions, with an average transit time of 5–15 days.
Manufacturer-Direct Value: By removing middlemen, we deliver fair pricing without compromising on materials or quality control.

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