Thermostat (60°C/140°F) – Fits Yamaha 4-Stroke 2.5-80 HP Outboards (Replaces 66M-12411-01-00, 66M-12411-00-00)

Thermostat (60°C/140°F) – Fits Yamaha 4-Stroke 2.5-80 HP Outboards

This thermostat is designed for a wide range of Yamaha 4-Stroke outboard engines, including models from 2.5 HP up to 80 HP. It regulates engine temperature by opening at 60°C (140°F) to allow coolant to circulate, ensuring optimal performance and preventing overheating.

This component is a direct replacement for Yamaha part numbers 66M-12411-01-00, 66M-12411-00-00, and older 6G8-12411-xx-xx series thermostats.

• Engineered for direct, hassle-free installation.
• Maintains a consistent operating temperature of 60°C (140°F).
• Features a small relief hole to improve water flow and cooling during idle.

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 Yamaha owners, here’s a guide to help you identify your engine’s serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Thermostat (66M-12411-01-00)

Installation Guide

1. Safety First: Ensure the engine is completely cool and disconnected from the battery before beginning.
2. Locate Housing: Find the thermostat housing on the engine block or cylinder head.
3. Remove Cover: Unscrew the bolts holding the thermostat cover in place. Note the position of the cover and gasket.
4. Extract Old Thermostat: Carefully remove the old thermostat from the housing. Take note of its orientation.
5. Clean Surfaces: Clean any old gasket material or corrosion from both the housing and cover mating surfaces.
6. Install New Thermostat: Place the new thermostat into the housing in the correct orientation. Ensure the small relief hole is positioned correctly, typically at the top.
7. Replace Gasket: Install a new thermostat gasket onto the housing.
8. Re-attach Cover: Secure the cover back onto the housing, tightening the bolts to the manufacturer's recommended torque specification in a crisscross pattern.
9. Reconnect and Test: Reconnect the battery. Start the engine and check for any leaks around the housing as the engine warms up.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my specific Yamaha engine?
A: The best way is to match your engine's original part number to the numbers in our cross-reference table. You can also check our compatible models list, but confirming the part number with your engine's service manual or parts diagram is the most reliable method.

Q: What are the common signs of a failing thermostat?
A: A faulty thermostat can either stick open, causing the engine to run too cool and perform poorly, or stick closed, leading to rapid overheating. An engine temperature alarm or an inconsistent temperature gauge reading are key indicators.

Q: How often should I replace my engine's thermostat?
A: Replacement intervals vary, but it's good practice to inspect it during regular cooling system service or every 2-3 years, especially if operating in saltwater. Replace it immediately if you suspect it is failing.

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.