8M0021043 Fuel & Water Sensor for Mercury Marine | JLM Marine

Fuel & Water Sensor for Mercury Marine 75-400HP Outboards

This Fuel and Water Sensor is designed for Mercury Marine outboard engines ranging from 75HP to 400HP. Engineered to detect water contamination in your fuel system, this sensor helps protect your engine from damage and ensures reliable performance on the water.

This aftermarket replacement directly replaces Mercury Marine part numbers 8M0021043, 8M0157779, and 889330, providing a cost-effective solution for maintaining your outboard's fuel system integrity.

• Direct replacement for Mercury Marine OEM sensors
• Detects water contamination in fuel system
• Compatible with 75-400HP Mercury 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.

Technical Specifications

Package Contents

Your package includes:

• 1 × Fuel and Water Sensor

Installation Guide

1. Disconnect the battery negative terminal to ensure safety during installation.
2. Locate the existing fuel and water sensor on your Mercury outboard fuel system.
3. Disconnect the electrical connector from the old sensor by pressing the release tab.
4. Use an appropriate wrench to carefully unscrew the old sensor from the fuel filter assembly.
5. Inspect the mounting threads and clean any debris or residue from the mounting area.
6. Hand-thread the new fuel and water sensor into the fuel filter assembly to avoid cross-threading.
7. Tighten the sensor to the manufacturer's recommended torque specification using a torque wrench.
8. Reconnect the electrical connector to the new sensor, ensuring it clicks securely into place.
9. Reconnect the battery negative terminal.
10. Turn the ignition key to the "ON" position and check that the sensor warning light functions properly.
11. Inspect for any fuel leaks around the sensor mounting area before starting the engine.
12. Start the engine and monitor the system for proper operation and no warning indicators.

Troubleshooting & FAQ

Q: How do I confirm this sensor fits my Mercury outboard?
A: This sensor is designed for Mercury Marine outboards rated between 75HP and 400HP. Check your engine's horsepower rating and verify the original part number (8M0021043, 8M0157779, or 889330) against your existing sensor to ensure compatibility.

Q: What are the signs that my fuel and water sensor needs replacement?
A: Common symptoms include a persistent water-in-fuel warning light, engine misfiring or hesitation, difficulty starting, or poor performance. If you notice any of these issues, inspect and test your fuel and water sensor.

Q: How often should I replace the fuel and water sensor?
A: The sensor typically does not require regular replacement unless it fails or becomes damaged. However, it should be inspected during routine maintenance and replaced if it shows signs of corrosion, physical damage, or fails diagnostic testing.

Q: Can I install this sensor myself, or do I need a professional?
A: If you have basic mechanical skills and the proper tools, you can install this sensor yourself by following the installation guide. However, professional installation is recommended to ensure proper torque, electrical connections, and system safety.

Q: OEM vs. Aftermarket?
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.