8M0251123 Water Pump Impeller Kit for Mercury Bigfoot Lightning Marathon Super15 SeaPro | JLM Marine

8M0251123 Water Pump Impeller Kit for Mercury Bigfoot Lightning Marathon Super15 SeaPro

This comprehensive water pump impeller kit is engineered for Mercury outboard motors including 13.5-15 HP Bigfoot, 20-25 HP 2-cylinder (serial 0P325500-1B000001 & Up), 25 HP Lightning 3-cylinder (serial 0E268781-0E288000), and 25 HP Marathon, Super15, and SeaPro 2-cylinder models. It delivers complete cooling system maintenance in a single package.

This kit directly replaces OEM part number 8M0251123, providing a cost-effective solution for routine water pump service and ensuring reliable cooling performance across multiple Mercury engine families.

• Includes 18 essential components: impeller, seals, gaskets, wear plate, housing, thermostat, fuel filters, and gear oil pump
• Covers complete cooling system rebuild with all necessary hardware and consumables
• Designed for Mercury 2-cylinder and 3-cylinder mid-range outboards

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.

Package Contents

This kit includes all components required for a complete water pump and cooling system service:

• 47-85089-10 Water Pump Impeller × 1
• 8M0032838 / 85119 Impeller Key × 1
• 85083 Wear Plate × 1
• 46-99157A02 Water Pump Housing × 1
• 27-99326-1 Gasket × 1
• 26-85090001 Seal × 1
• 25-86203 Seal × 1
• 12-86645-1 Washer × 2
• 23-85095 Insulator × 4
• 12-191833 Drain Screw Gasket × 3
• 25-69202 O-Ring × 1
• 25-62702 O-Ring × 2
• 14586 Thermostat × 1
• 27-8M0177107 Gasket × 1
• 35-87946Q3 Fuel Filter × 1
• 35-816296Q03 Fuel Filter × 1
• 27-828816 Oil Drain Screw Gasket × 1
• 24OP149 Gear Oil Pump × 1

Installation Guide

1. Disconnect the fuel line and remove the engine cowling to access the lower unit. Tilt the engine fully up and drain the gear oil using the drain screw and new gasket provided.
2. Remove the lower unit by loosening the mounting bolts and carefully separating it from the mid-section. Be cautious of the shift rod and water tube connections.
3. Disassemble the old water pump housing by removing the mounting screws. Extract the old impeller, wear plate, seals, and gaskets; discard all worn components.
4. Clean all mating surfaces thoroughly to remove old gasket material, corrosion, and debris. Inspect the water pump base for damage or excessive wear.
5. Install the new wear plate (85083) onto the pump base, ensuring proper alignment. Apply a thin layer of marine grease to facilitate smooth assembly.
6. Lubricate the new impeller (47-85089-10) with glycerin or soapy water, then carefully insert it into the housing with the impeller key (8M0032838) positioned correctly in the drive shaft slot.
7. Install the new water pump housing (46-99157A02) over the impeller, ensuring all blades flex in the correct direction. Use the new gasket (27-99326-1) and tighten mounting screws evenly in a cross pattern.
8. Replace all seals and O-rings (26-85090001, 25-86203, 25-69202, 25-62702) at their respective locations on the drive shaft and housing interfaces.
9. Install the new thermostat (14586) with its gasket (27-8M0177107) into the thermostat housing, ensuring the spring side faces the correct direction per your service manual.
10. Reattach the lower unit to the mid-section, aligning the shift rod and water tube carefully. Tighten all mounting bolts to factory torque specifications.
11. Refill the gear oil using the provided gear oil pump (24OP149) until oil flows from the upper vent hole. Install new drain screw gaskets (12-191833, 27-828816) and tighten plugs securely.
12. Replace fuel filters (35-87946Q3, 35-816296Q03) in their respective housings, reconnect fuel lines, and test-run the engine in water to verify proper cooling flow from the telltale indicator.

Troubleshooting & FAQ

Q: How do I confirm this kit fits my Mercury engine?
A: Cross-reference your engine's model and serial number with the compatibility table above. For Mercury engines, check the serial number plate on the transom bracket or use the Mercury Serial Number Guide to verify your exact model. If your serial number falls within the ranges listed (e.g., 0P325500-1B000001 & Up for 20-25 HP models), this kit will fit.

Q: How often should I replace the water pump impeller?
A: Mercury recommends replacing the water pump impeller every 2-3 years or 300 hours of operation, whichever comes first. If you operate in sandy or silty water, inspect it annually and replace if any blades show cracking, wear, or deformation.

Q: What are the signs that my water pump is failing?
A: Common symptoms include weak or no water flow from the telltale (indicator stream), engine overheating warnings, reduced performance, or steam from the engine. If you notice any of these, shut down immediately and inspect the water pump system.

Q: Why does this kit include fuel filters and a gear oil pump?
A: This is a comprehensive service kit designed to address multiple maintenance items during lower unit service. Replacing fuel filters and servicing gear oil during water pump replacement ensures complete routine maintenance and prevents additional disassembly later.

Q: Can I reuse the old gaskets and seals if they look okay?
A: No, always replace all gaskets, seals, and O-rings during water pump service. Even if they appear intact, compressed gaskets lose their sealing ability and can cause leaks or overheating. All necessary seals and gaskets are included in this kit.

Q: What is the difference between this aftermarket kit and the OEM Mercury kit?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out 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.