Thermostat Assembly – Fits Yamaha Outboard 2.5-100HP (Replaces Yamaha 66M-12411-01-00)
Thermostat Assembly – Fits Yamaha Outboard 2.5-100HP (Replaces Yamaha 66M-12411-01-00) is backordered and will ship as soon as it is back in stock.
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Thermostat Assembly – Fits Yamaha Outboard 2.5-100HP (Replaces Yama...
Thermostat Assembly – Fits Yamaha Outboard 2.5-100HP (Replaces Yamaha 66M-12411-01-00) is backordered and will ship as soon as it is back in stock.
Product Details
This Yamaha Thermostat Assembly is an essential component designed to maintain proper engine operating temperature by regulating coolant flow. It is engineered for a wide range of Yamaha 4-Stroke Outboards from 2.5 HP to 100 HP, covering models from approximately 1996 to 2023.
It serves as a direct replacement for Yamaha OEM part 66M-12411-01-00 and interchanges with aftermarket references like GHmarine 66M-12411 and PWCParts 66M-12411-01-00.
- Installs as a direct OEM-equivalent replacement.
- Opens at a specified 60°C (140°F) to regulate engine temperature.
- Built as a critical component for the engine's cooling system health.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 66M-12411-01-00 |
| GHmarine | 66M-12411 |
| PWCParts | 66M-12411-01-00 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Yamaha Outboard Models:
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | F2.5 | 2.5 | 4-Stroke | 2003–2023 | 66M-12411-01-00 | |
| Yamaha | F4/F4A | 4 | 4-Stroke | 1999–2016 | 66M-12411-01-00 | |
| Yamaha | F6/F6A | 6 | 4-Stroke | 2000–2016 | 66M-12411-01-00 | |
| Yamaha | F8/T8 | 8 | 4-Stroke | 2001–2016 | 66M-12411-01-00 | |
| Yamaha | F9.9/T9.9 | 9.9 | 4-Stroke | 1985–2023 | 66M-12411-01-00 | Multiple model variants |
| Yamaha | F15/T15 | 15 | 4-Stroke | 1998–2023 | 66M-12411-01-00 | |
| Yamaha | F25/T25 | 25 | 4-Stroke | 1998–2019 | 66M-12411-01-00 | |
| Yamaha | F30 | 30 | 4-Stroke | 2001–2023 | 66M-12411-01-00 | |
| Yamaha | F40/T40 | 40 | 4-Stroke | 1999–2023 | 66M-12411-01-00 | Various model variants including F40A, F40B |
| Yamaha | F50/T50 | 50 | 4-Stroke | 1995–2023 | 66M-12411-01-00 | |
| Yamaha | F60/T60 | 60 | 4-Stroke | 2002–2023 | 66M-12411-01-00 | |
| Yamaha | F70 | 70 | 4-Stroke | 2010–2023 | 66M-12411-01-00 | |
| Yamaha | F80 | 80 | 4-Stroke | 66M-12411-01-00 | ||
| Yamaha | F100 | 100 | 4-Stroke | Up to 2000 | 66M-12411-01-00 |
Technical Specs
- Product Type
- Thermostat Assembly
- Installation
- Direct OEM replacement
- Operating Temperature
- 60°C (140°F) opening temperature
- Housing Material
- Metal
- Housing Color
- Silver/Metallic
- Warranty
- OEM Yamaha warranty when purchased from authorized dealer
- Other Technical Attributes
- Critical cooling system component that opens at specified temperature to allow coolant flow
What’s in the Box
- 1 x Thermostat (66M-12411-01-00)
Installation Notes
- Ensure the engine is completely cool before starting.
- Disconnect the battery to prevent any accidental starts.
- Place a drain pan under the engine and drain the coolant.
- Locate the thermostat housing on the engine block or cylinder head.
- Remove the bolts securing the housing cover and carefully lift it away.
- Note the orientation of the old thermostat before removing it.
- Clean the mating surfaces of the housing and cover, removing all old gasket material.
- Install the new thermostat in the correct orientation. Replace the gasket if it is worn or not included.
- Re-secure the housing cover and torque the bolts to the manufacturer's specification.
- Refill the cooling system with the recommended coolant type.
- Reconnect the battery, start the engine, and let it reach operating temperature.
- Carefully check for any leaks around the thermostat housing.
Troubleshooting & FAQ
How do I know if my thermostat is failing?
Common signs of a failing thermostat include engine overheating (stuck closed) or taking too long to reach operating temperature (stuck open). You may also notice erratic temperature gauge readings or coolant leaks around the housing.
What temperature does this thermostat open at?
This thermostat is designed to begin opening at 60°C (140°F), as per OEM specifications, to allow coolant to circulate through the engine.
My engine model is listed, how can I be sure it fits?
While this part fits a wide range of models, we recommend visually comparing your old thermostat to the product images and confirming the part number (66M-12411-01-00) in your engine's service manual. Year splits can be complex, so verification is key.
Does this assembly include a new gasket?
This package contains the thermostat only. Gaskets are often replaced during this job but are not included in this specific package. Please check if you need to source one separately.
Can I test my old thermostat or this new one before installation?
Yes. You can suspend the thermostat in a pot of water with a thermometer. Heat the water and observe the temperature at which the thermostat begins to open. It should start opening around its rated temperature of 60°C (140°F).
What is the difference between OEM and this aftermarket part?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials and functionality. Our parts are manufactured in an ISO 9002 facility and are batch-inspected for quality and consistency.
How fast is shipping?
We ship worldwide quickly—typical transit is 5–15 days for most regions. Standard shipping is free, and expedited options may be available at checkout depending on your location.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter an issue, please contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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