Thermostat – Fits Yamaha 4-Stroke 80-100HP (Replaces 6D9-12411-00)
Thermostat – Fits Yamaha 4-Stroke 80-100HP (Replaces 6D9-12411-00) is backordered and will ship as soon as it is back in stock.
Couldn't load pickup availability
Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Product Details
This is a replacement Thermostat – Fits Yamaha 4-Stroke 80-100HP (Replaces 6D9-12411-00), designed for F80 to F100 series outboard motors from approximately 2005 to 2017. It ensures your engine maintains the correct operating temperature of 55°C (131°F) for optimal performance and fuel efficiency.
This part is a direct interchange for Yamaha part number 6D9-12411-00 and Sierra 18-3639.
- Installs as a direct replacement for the OEM thermostat.
- Regulates engine temperature to a factory-rated 55°C (131°F).
- Package includes one thermostat, ready for installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 6D9-12411-00 |
| Sierra | 18-3639 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Yamaha owners, please cross-reference your engine's model and year to ensure a precise match. The OEM part number 6D9-12411-00 is associated with all listed models.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. |
|---|---|---|---|---|---|
| Yamaha | F100DET | 100 | 4-Stroke | 2005–2014 | 6D9-12411-00 |
| Yamaha | F100L | 100 | 4-Stroke | 2015–2017 | 6D9-12411-00 |
| Yamaha | F100X | 100 | 4-Stroke | 2015–2017 | 6D9-12411-00 |
| Yamaha | F100D | 100 | 4-Stroke | 2005 & Later | 6D9-12411-00 |
Technical Specs
- Product Type
- Marine Engine Thermostat
- Installation
- Direct replacement
- Operating Temperature
- 55°C (131°F)
- Housing Color
- Silver/metallic
- Dimensions
- 6.0 x 6.0 x 6.0
What’s in the Box
- 1 x Thermostat (6D9-12411-00)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery.
- Locate the thermostat housing on the engine block. Place a drain pan underneath.
- Carefully remove the bolts securing the housing cover. Note the orientation of the housing.
- Remove the old thermostat and the gasket. You may need to gently pry it out.
- Thoroughly clean the mating surfaces of the housing and cover, removing all old gasket material.
- Install the new thermostat in the correct orientation. A new gasket is highly recommended.
- Reinstall the housing cover and tighten the bolts to the manufacturer's specified torque.
- Reconnect the battery, refill the cooling system, and check for leaks after starting the engine.
Troubleshooting & FAQ
How do I know if this thermostat fits my Yamaha outboard?
The best way to confirm fitment is to check the part number (6D9-12411-00) against your service manual or current thermostat. You can also use our compatibility table to match your engine's model and year range.
What are the signs of a faulty thermostat?
Common signs include engine overheating (stuck closed) or taking too long to reach operating temperature (stuck open). Inconsistent temperature gauge readings are another indicator.
What is the operating temperature of this thermostat?
This thermostat is designed to open at 55°C (131°F), matching OEM specifications to ensure your engine runs in its optimal temperature range.
Do I need a new gasket for installation?
Yes, it is always highly recommended to use a new thermostat housing gasket during installation to ensure a proper seal and prevent coolant leaks.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in 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.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
