Thermostat (60°C/140°F) – Fits Mercury/Mariner 75-225 HP Outboard Engines (Replaces 8M0175321, 855676004, 8M6010296)

Thermostat (60°C/140°F) – Fits Mercury/Mariner 75-225 HP Outboard Engines

This thermostat is designed for a direct fit on Mercury and Mariner outboard engines, including 75 HP, 80 HP, 90 HP, 100 HP, and 225 HP 4-stroke models. It is compatible with specific models based on the serial number ranges provided in the compatibility table.

This component directly replaces Mercury part numbers 855676004, 8M0175321, 8M6010296, 8556761, and Sierra 18-3632.

• Engineered for direct OEM replacement to ensure proper fit and function.
• Maintains optimal engine temperature with a specified 60°C (140°F) opening temperature.
• Constructed with a durable brass and stainless steel housing for corrosion resistance in marine environments.

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 60°C (140°F) Thermostat (Replaces 855676004/8M0175321/8M6010296)

Installation Guide

1. Disconnect Power: Ensure the engine is off and cool, then disconnect the battery terminals to prevent accidental starts.
2. Drain Coolant: Place a container under the engine and carefully drain the coolant from the system.
3. Locate Housing: Identify the thermostat housing on the engine block. It is typically a metal cover with a coolant hose attached.
4. Remove Housing: Loosen and remove the bolts securing the thermostat housing. Gently tap the housing if it's stuck, but avoid prying.
5. Remove Old Thermostat: Lift out the old thermostat and its gasket or seal. Note its orientation.
6. Clean Surfaces: Thoroughly clean the mounting surfaces of the housing and engine block, removing all old gasket material and corrosion.
7. Install New Thermostat: Place the new thermostat into the engine block in the correct orientation. Install the new gasket or seal.
8. Reassemble: Re-attach the housing and tighten the bolts to the manufacturer's recommended torque specifications.
9. Refill Coolant: Reconnect all hoses and refill the cooling system with the appropriate type and amount of coolant.
10. Check for Leaks: Reconnect the battery, start the engine, and let it warm up. Carefully check for any coolant leaks around the housing.

Troubleshooting & FAQ

How do I confirm this fits my engine?
The best way to confirm fitment is by matching your engine's serial number to the ranges listed in the "Compatible Engine Models" table. Also, compare your original part to our product images and the listed OEM replacement numbers (855676004, 8M0175321, 8M6010296) to ensure a match.

What are the symptoms of a failing thermostat?
Common signs include the engine overheating or, conversely, not reaching its proper operating temperature. You may also notice fluctuating temperature gauge readings or poor engine performance.

Why is the 60°C/140°F temperature rating important?
This specific temperature rating ensures your engine warms up quickly and maintains the optimal temperature for efficient combustion, performance, and longevity, as designed by the manufacturer.

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.