Water Pump Impeller Kit – Fits Mercury Marine 25-50 HP, Force 40-50 HP (Replaces 821354A2, 821354A1, 821354A04, 18-4531)

$29.68 $47.00

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Water Pump Impeller Kit – Fits Mercury Marine 25-50 HP, Force 40-50 HP (Replaces 821354A2, 821354A1, 821354A04, 18-4531) is backordered and will ship as soon as it is back in stock.

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You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

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Delivery and Shipping

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This Water Pump Impeller Kit – Fits Mercury Marine 25-50 HP (Replaces 821354A2, 821354A1) provides all the necessary components for a complete water pump overhaul. It is designed for Mercury Marine 25-50 HP 4-Stroke outboards from 1998 and newer, including 25, 30, 40, 45, and 50 HP models. It also fits select Force 40/50 HP engines from 1995–1997.

This kit serves as a direct replacement for Mercury/Quicksilver part numbers 821354A1, 821354A2, 821354A04 and aftermarket equivalents from Sierra (18-4531) and GLM (12045).

Installs in the lower unit (gearcase) to restore cooling system performance.
Constructed from durable materials, including a neoprene impeller and stainless steel wear plate.
Includes all required gaskets, seals, and hardware for a complete service.

Part Number Matrix

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

Brand	Part Number
Mercury/Quicksilver	821354A1
Mercury/Quicksilver	821354A2
Mercury/Quicksilver	821354A04
Sierra	18-4531
GLM	12045

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This kit is verified to fit the following Mercury Marine outboard models.

This kit is also compatible with select Force outboard models.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	25 FourStroke Carb	25	4-Stroke	1998–Up	821354A2	Serial: 0G590000-0T408999
Mercury	30 Four Stroke Carb	30	4-Stroke	1998–Up	821354A2	Serial: 0G760300-0T408999
Mercury	30 Jet	30	4-Stroke	1998–Up	821354A2	Serial: 0G590000 & Up
Mercury	30 (2 Cyl)	30	2-Stroke	1994–1998	821354A2	Serial: 0G053314-0T598999
Mercury	40 (2 Cyl)	40	2-Stroke	1994–Up	821354A2	Serial: 0G053314 & Up
Mercury	40/45 Four Stroke 2:1	40/45	4-Stroke	1998–Up	821354A2	Serial: 0G760300-0T408999
Mercury	45 Four Stroke Bodensee	45	4-Stroke	1996–1998	821354A2	Serial: 0G231123-0T178499
Mercury	40 (3 Cyl)	40	4-Stroke	1997–1998	821354A2	Serial: 0G531301 & Up
Mercury	50 (3 Cyl)	50	4-Stroke	1998–Up	821354A2	Serial: 0G590000 & Up
Mercury	50 Four Stroke	50	4-Stroke	1995–1998	821354A2	Serial: 0G231123-0T178499
Mercury	50 Bigfoot	50	4-Stroke	1998–Up	821354A2
Force	40	40	2-Stroke	1995-1997	821354A2
Force	50	50	2-Stroke	1995-1997	821354A2

Technical Specs

Product Type: Water Pump Impeller Kit
Installation: Lower Unit / Gearcase
Material: Neoprene Impeller, Stainless Steel Wear Plate, Nylon PA66 Tube, Non-asbestos Gasket
Dimensions: 152.4 mm × 114.3 mm × 49.0 mm (6.0 in × 4.5 in × 1.93 in)
Weight: 0.17 kg (0.39 lb)
OEM Part Number: Mercury Marine 821354A2

What’s in the Box

1 x Tube Seal (700-85180)
1 x Tube Seal (700-85181)
1 x Washer (700-31175/12-86645)
1 x Water Pump Impeller (700-89640/47-85089)
1 x Gasket Upper (700-37490/27-822189)
1 x Wear Plate (700-12505/8213542)
1 x Gasket Lower (700-37700/27-822217)
1 x Drive Key (85119)

Installation Notes

Disconnect the battery and ignition system for safety.
Drain the gearcase oil into a suitable container.
Unbolt and carefully remove the lower unit (gearcase) from the outboard's driveshaft housing.
Remove the bolts securing the water pump housing cover.
Slide the housing up and off, then remove the old impeller, key, gaskets, and wear plate.
Thoroughly clean the housing and base surfaces, removing any old gasket material or debris.
Install the new components from the kit in reverse order: wear plate, gasket, key, impeller (turn driveshaft clockwise to seat vanes), and seals.
Reinstall the water pump housing and torque bolts to manufacturer specifications.
Re-mount the lower unit, ensuring the driveshaft, shift shaft, and water tube are correctly aligned.
Refill the gearcase with fresh marine gear lube.
Test the engine in water, verifying a strong stream from the telltale outlet.

Troubleshooting & FAQ

How do I know if this kit fits my engine?

First, check the compatibility table and see if your engine's model, HP, and year range are listed. For absolute certainty, match your engine's serial number to the ranges in the "Notes" column. If you are still unsure, compare the parts pictured in our listing to your existing parts before ordering.

What are the signs of a failing water pump impeller?

The most common indicators of a worn or damaged impeller are engine overheating at idle or low speeds, a weak or intermittent water stream from the tell-tale port, or finding bits of black rubber in the cooling passages. A visual inspection will often reveal cracked, broken, or missing vanes on the impeller itself.

How often should I replace my water pump impeller?

For preventative maintenance, it is recommended to inspect your impeller annually and replace it every 1 to 2 years, or every 100-200 hours of operation. Replacement frequency should be increased if you operate in saltwater or shallow, sandy/silty conditions, as these environments accelerate wear.

The kit includes two different tube seals. Which one do I use?

The kit is designed to cover multiple engine variations, which may use different size seals. Compare the new seals directly against the original seal you removed from your water tube and install the one that is an exact match.

Is this kit the same quality as the original OEM part?

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

How fast is shipping and what does it cost?

We ship worldwide quickly—typical transit time is 5–15 days. Standard shipping is free to most regions, with expedited options available at checkout where applicable.

What is the warranty and return policy?

This part is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter an issue, please contact our support team with your order details. Returns are accepted within our standard window, provided the item is unused and in its 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.

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