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

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

This water pump impeller kit provides the necessary components to service the lower unit water pump on a range of Mercury, Mariner, and Force outboard engines. It is designed for Mercury/Mariner 25-50 HP 4-Stroke models (1998 and newer) and also fits select Force 40-50 HP 2-Stroke models (1995-1997).

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

• Complete Service Kit: Includes a durable neoprene impeller, stainless steel wear plate, gaskets, seals, and drive key for a full replacement.
• Core Materials: Features a high-quality neoprene rubber impeller for reliable water flow and a corrosion-resistant stainless steel wear plate.
• Direct Fit Installation: All components are manufactured to OEM specifications for a direct fit in the engine's lower unit water pump housing.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Water Pump Impeller (Replaces 47-85089, 8M0027792)
• 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)
• 2 x Washer (12-86645)

Installation Guide

1. Prepare the Engine: Disconnect the battery and shift the outboard into the neutral position.
2. Remove Lower Unit: Unbolt the lower unit (gearcase) from the engine's midsection and carefully disconnect the shift linkage.
3. Access Water Pump: Place the lower unit on a suitable workbench and remove the bolts securing the water pump housing cover.
4. Expose Impeller: Lift the housing straight up to expose the old impeller. Take note of the rotational direction of the existing impeller's fins.
5. Remove Old Components: Remove the old impeller, drive key, wear plate, gaskets, and seals from the housing and driveshaft.
6. Clean Surfaces: Thoroughly clean all mating surfaces on the housing and base, removing any old gasket material, sealant, or corrosion.
7. Install New Base Components: Install the new lower gasket and the stainless steel wear plate onto the pump base.
8. Install New Impeller: Slide the new impeller drive key onto the driveshaft flat. Apply a light lubricant to the new impeller and slide it down the shaft while turning clockwise to correctly orient the fins inside the housing.
9. Reassemble Housing: Apply sealant to the new upper gasket, place it on the housing, and reinstall the housing cover.
10. Torque Bolts: Tighten the water pump housing bolts to the manufacturer's recommended torque specification in a crisscross pattern.
11. Reinstall Lower Unit: Re-attach the lower unit to the engine, making sure the water tube and shift linkage are properly aligned.
12. Test Operation: Once fully assembled, start the engine using a water supply (flushing attachment) and confirm a steady water stream from the "telltale" outlet.

Troubleshooting & FAQ

Q: How do I confirm this kit will fit my engine?

A: The most reliable method is to check your engine's model and serial number against the "Compatible Engine Models" table. For Mercury and Mariner engines, the serial number range is critical for ensuring an exact match. We provide a link to the official Mercury Serial Number Guide to help you with identification.

Q: What are the signs of a failing water pump impeller?

A: The most common symptom is a weak or non-existent water stream from the engine's "telltale" outlet, which indicates poor cooling. Other signs include engine overheating alarms at idle or low speeds, or finding brittle, cracked, or missing vanes on the old impeller during an inspection.

Q: How often should I replace my water pump impeller?

A: As a general rule, it is best to inspect the impeller annually and replace it every 1-2 years or 100-200 hours of use. If you frequently operate in sandy, silty, or saltwater environments, more frequent replacement (every year) is recommended to prevent premature failure.

Q: Is this an OEM part or an aftermarket one?

A: This listing is for an aftermarket replacement part, not an OEM component. Our parts are manufactured to meet or exceed OEM specifications using high-quality, comparable-grade materials. Production occurs in an ISO9002-certified facility where each batch is inspected to ensure consistent quality and performance.

Q: How fast do you ship and what are the costs?

A: We offer fast global shipping, with most orders arriving within 5–15 days worldwide. Standard shipping is free for all orders. Expedited shipping options are also available at checkout and vary depending on your location.

Q: What is your warranty and return policy?

A: This product is covered by a 1-year warranty against any manufacturing defects under normal operating conditions. If you encounter an issue, please contact our support team with your order details. Returns are accepted within our standard return window for unused items in their original condition; please see our official policy page or contact us for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.