8M0251122 Service Kit for Mercury 15HP 18HP | JLM Marine

8M0251122 Service Kit for Mercury 15HP 18HP | JLM Marine

This comprehensive service kit is engineered for Mercury 15HP and 18HP outboard engines, specifically the 18HP 2-cylinder International models (serial number 0N001590 & Up) and 15HP Japanese models. It includes all essential components for routine maintenance—impeller, thermostat, gaskets, fuel filter, anode, and fasteners—to keep your engine running at peak performance.

Direct Replacement for OEM Part Number: 8M0251122. This aftermarket kit delivers OEM-equivalent fit and function at a competitive price, ensuring reliable service intervals for your Mercury outboard.

• Complete 13-piece service kit with impeller, thermostat, fuel filter, and all necessary gaskets
• Includes gear oil pump and anode for comprehensive maintenance coverage
• Designed for Mercury 2-cylinder outboards with serial number 0N001590 and up

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

This service kit includes the following components:

• 8M0075040 – Gasket × 1
• 803753 – Guide Plate × 1
• 803751 – Insert × 1
• 803749 – Key × 1
• 803748 – Impeller × 1 (critical wear component)
• 823042046 – Screw × 3
• 804540 – Thermostat × 1
• 27-853702005 – Thermostat Gasket × 1
• 35-8M0088825 – Fuel Filter × 1
• 12-191833 – Drain Screw Gasket × 3
• 27-828816 – Oil Drain Screw Gasket × 1
• 803731 – Anode × 1
• 24OP149 – Gear Oil Pump × 1

Installation Guide

Follow these steps to install the service kit components. Always refer to your Mercury service manual for model-specific procedures:

1. Preparation: Disconnect the fuel line and remove the lower unit from the engine according to your service manual. Drain all gear oil into a suitable container.
2. Remove Old Impeller: Access the water pump housing and carefully extract the old impeller (803748), guide plate (803753), and insert (803751). Inspect the housing for wear or damage.
3. Clean Surfaces: Thoroughly clean all gasket surfaces on the pump housing and lower unit. Remove old gasket material to ensure proper sealing.
4. Install New Impeller Assembly: Lubricate the new impeller with glycerin or soapy water, then install it with the key (803749), insert, and guide plate in the correct orientation.
5. Replace Thermostat: Remove the old thermostat (804540) from its housing and clean the mating surface. Install the new thermostat with a fresh gasket (27-853702005).
6. Install Gaskets: Position the new water pump gasket (8M0075040) on the lower unit housing. Ensure proper alignment before reassembly.
7. Reassemble Lower Unit: Carefully reinstall the lower unit onto the engine, torquing all screws (823042046) to factory specifications.
8. Replace Drain Screw Gaskets: Install new drain screw gaskets (12-191833) and oil drain screw gasket (27-828816) on all drain plugs before refilling.
9. Refill Gear Oil: Use the included gear oil pump (24OP149) to refill the lower unit with Mercury Premium Gear Lube or equivalent. Fill until oil appears at the upper vent hole.
10. Replace Fuel Filter: Locate the inline fuel filter and replace it with the new filter (35-8M0088825). Ensure all connections are secure and free of leaks.
11. Install Anode: Replace the old anode (803731) with the new one, ensuring proper electrical contact for corrosion protection.
12. Test Run: Reconnect the fuel line, prime the system, and run the engine in a test tank or on-water. Check for proper water flow from the tell-tale and inspect for any leaks.

Troubleshooting & FAQ

Q: How do I confirm this kit fits my Mercury engine?
A: Check your engine's serial number plate—this kit fits 18HP 2-cylinder International models with serial number 0N001590 and up, as well as 15HP Japanese models. Cross-reference your serial number with the compatibility table above or consult your Mercury dealer.

Q: How often should I replace the impeller and service components?
A: Mercury recommends replacing the water pump impeller every 2–3 years or 200–300 hours of operation, whichever comes first. The thermostat, fuel filter, and gaskets should be replaced at the same interval or if you notice overheating, poor water flow, or fuel delivery issues.

Q: What are the signs that my impeller or thermostat has failed?
A: Common symptoms include weak or no water flow from the tell-tale, engine overheating alarms, steam from the engine, or reduced cooling performance. If you notice any of these, inspect and replace the impeller and thermostat immediately to prevent engine damage.

Q: Can I reuse the old gaskets and screws?
A: No, always replace gaskets with new ones to ensure proper sealing and prevent leaks. The kit includes all necessary gaskets and screws—reusing old components can lead to water intrusion, oil leaks, and premature part failure.

Q: What type of gear oil should I use with the included pump?
A: Use Mercury Premium Gear Lube or a high-quality marine gear oil rated for outboard lower units. The included pump (24OP149) makes refilling easy and minimizes mess.

Q: Is this an OEM or aftermarket part?
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.