8M2003959 Oxygen Sensor for Mercruiser 3.0L 4.3L 4.5L 5.0L 5.7L 6.2L 8.1L 8.2L | JLM Marine

Oxygen Sensor for Mercruiser 3.0L 4.3L 4.5L 5.0L 5.7L 6.2L 8.1L 8.2L – OEM 8M2003959

This aftermarket oxygen sensor is engineered to replace OEM part number 8M2003959 for a wide range of Mercruiser sterndrive and inboard engines. It delivers reliable exhaust monitoring and fuel management across 3.0L, 4.3L, 4.5L, 5.0L, 5.7L, 6.2L, 8.1L, and 8.2L engine families, ensuring accurate air-fuel ratio feedback for optimal performance and emissions control.

This sensor directly replaces Mercruiser part numbers 710-8M2003959 and 8M2003959, providing a cost-effective alternative to OEM components without sacrificing reliability or precision.

• Drop-in replacement for Mercruiser oxygen sensors on MPI and Mag series engines
• Designed for sterndrive and inboard applications across multiple displacement ranges
• Ensures accurate exhaust gas monitoring for improved fuel economy and engine efficiency

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.

Technical Specifications

Package Contents

• 1 × Oxygen Sensor (OEM 8M2003959)

Installation Guide

1. Disconnect the negative battery cable to prevent electrical shorts during installation.
2. Allow the engine to cool completely before attempting to remove the old oxygen sensor.
3. Locate the oxygen sensor on the exhaust manifold or exhaust system—refer to your engine's service manual for exact positioning.
4. Disconnect the electrical connector from the old sensor by carefully releasing the locking tab.
5. Using an appropriate oxygen sensor socket or wrench, unthread the old sensor counterclockwise and remove it from the exhaust port.
6. Inspect the threads in the exhaust port for debris or damage; clean if necessary using a thread chaser or wire brush.
7. Apply a small amount of anti-seize compound to the threads of the new oxygen sensor (avoid getting compound on the sensor tip).
8. Hand-thread the new sensor into the exhaust port clockwise, then tighten to the manufacturer's specified torque (typically 30–40 ft-lbs).
9. Reconnect the electrical connector to the new sensor, ensuring it clicks securely into place.
10. Reconnect the negative battery cable and start the engine to verify proper operation.
11. Check for exhaust leaks around the sensor installation point and confirm that no warning lights appear on the instrument panel.
12. Test-run the engine under normal operating conditions to ensure the sensor is providing accurate feedback to the ECM.

Troubleshooting & FAQ

How do I confirm this oxygen sensor fits my Mercruiser engine?
Verify your engine model and displacement against the compatibility table above. Cross-check the OEM part number 8M2003959 in your service manual or parts diagram to ensure it matches your current sensor.

What are the signs that my oxygen sensor needs replacement?
Common symptoms include poor fuel economy, rough idling, sluggish acceleration, black exhaust smoke, or a Check Engine light. A failing sensor may also cause the engine to run too rich or too lean.

How often should I replace the oxygen sensor?
Oxygen sensors typically last 50,000–100,000 miles or 3–5 years, depending on operating conditions. Replace sooner if you notice performance issues or if the sensor is fouled by oil, coolant, or carbon buildup.

Can I use anti-seize on the sensor threads?
Yes, apply a light coat of high-temperature anti-seize to the threads (avoid the sensor tip). This prevents thread galling and makes future removal easier, especially in marine environments prone to corrosion.

Will this aftermarket sensor work the same as the OEM part?
Yes, this sensor is built to OEM specifications and provides the same voltage output and response time. It integrates seamlessly with your Mercruiser ECM for accurate air-fuel ratio control.

OEM vs. Aftermarket?
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.

How fast do you ship and how much does it cost?
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.

What is your warranty and return policy?
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.