Thermostat (130°F/54°C) – Fits Mercury/Mariner 200-300 HP (Replaces 885599003, 885599004, 8M0057307)

Thermostat (130°F/54°C) – Fits Mercury/Mariner 200-300 HP

This thermostat is designed for a wide range of Mercury/Mariner 200-300 HP, 3.0L/3.2L 6-cylinder EFI, DFI, Optimax, Pro XS, and XS engines from 2002–2017. It ensures your engine maintains the correct operating temperature for optimal performance and longevity.

It serves as a direct replacement for Mercury part numbers 885599003, 885599004, and 8M0057307, as well as aftermarket parts Sierra 18-3535 and WSM 775-15.

• Operating Temperature: Opens at 130°F (54°C)
• Installation Method: Direct OEM Replacement
• Included Components: 1x Thermostat

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 Thermostat (885599003/885599004/8M0057307)

Installation Guide

1. Ensure the engine is completely cool before beginning.
2. Locate the thermostat housing, typically on top of the engine block or near the cylinder heads.
3. Place a container underneath and drain the engine coolant to a level below the thermostat housing.
4. Carefully remove the bolts securing the housing cover.
5. Take out the old thermostat and gasket. Note the orientation of the thermostat.
6. Thoroughly clean the mating surfaces of the housing and cover, removing any old gasket material.
7. Install the new thermostat in the same orientation as the original.
8. Place the new gasket into position on the housing.
9. Re-install the housing cover and tighten the bolts to the manufacturer's recommended torque.
10. Refill the cooling system with the appropriate coolant.
11. Start the engine, let it warm up, and carefully check for any leaks around the thermostat housing.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my engine?

A: Check your engine model, horsepower, and year against the "Compatible Engine Models" table. For Mercury owners, using the provided serial number guide is highly recommended. The most reliable method is to cross-reference your old part number with those listed in our "Part Number Cross-Reference" table.

Q: What are the signs of a failing thermostat?

A: Common signs include engine overheating, the engine running too cold (failing to reach normal operating temperature), erratic temperature gauge readings, poor engine performance, and increased fuel consumption.

Q: What is the operating temperature of this thermostat?

A: This thermostat is designed to begin opening at 130°F (54°C) to regulate the engine's operating temperature for peak efficiency and 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.