Yamaha Thermostat Assembly – Fits Yamaha Outboard 9.9-100HP (Replaces 66M-12411-01-00)

Yamaha Thermostat Assembly – Fits Yamaha Outboard 9.9-100HP (Replaces 66M-12411-01-00)

This thermostat assembly is designed for a wide range of Yamaha 4-Stroke outboards, from 2.5HP to 100HP, models from 1996 to 2023. It plays a critical role in your engine's cooling system by regulating coolant flow to maintain the proper operating temperature.

This component is a direct replacement for several OEM and aftermarket part numbers, ensuring a precise fit and function.

• Installation Method: Direct OEM replacement
• Operating Temperature: Opens at 60°C (140°F) to initiate coolant flow.
• Function: Regulates engine temperature by controlling the flow of coolant.

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 disconnect the battery before starting.
2. Drain Coolant: Place a drain pan under the engine and carefully drain the cooling system.
3. Locate Housing: Identify the thermostat housing on the engine block or cylinder head.
4. Remove Housing: Loosen and remove the bolts securing the thermostat housing cover.
5. Remove Old Thermostat: Take out the old thermostat and any existing gasket or seal. Note the orientation of the old thermostat.
6. Clean Surfaces: Thoroughly clean the mating surfaces of the housing and cover, removing all old gasket material.
7. Install New Thermostat: Place the new thermostat into the housing in the correct orientation. Install the new gasket or seal.
8. Reassemble: Reattach the housing cover and tighten the bolts to the manufacturer's specified torque.
9. Refill Coolant: Refill the cooling system with the recommended coolant type.
10. Final Checks: Reconnect the battery, start the engine, and carefully check for any leaks around the housing. Allow the engine to reach operating temperature to ensure the thermostat opens correctly.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my engine?
A: Verify your engine's model, HP, and year against the "Compatible Engine Models" table. For precise verification, use the linked Yamaha Serial Number Guide to identify your model and cross-reference the OEM part number.

Q: What are the signs of a failing thermostat?
A: Common symptoms include engine overheating (if the thermostat is stuck closed) or the engine taking an unusually long time to warm up to its proper operating temperature (if it is stuck open).

Q: At what temperature does this thermostat open?
A: This thermostat is designed to begin opening at 60°C (140°F), which is the standard specification for these Yamaha models to ensure optimal engine performance and efficiency.

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.