Thermostat – Fits Yamaha 2-Stroke 9.9-55 HP (Replaces 6F5-12411-01/6F5-12411-02/6F5-12411-03)
Thermostat – Fits Yamaha 2-Stroke 9.9-55 HP (Replaces 6F5-12411-01/6F5-12411-02/6F5-12411-03) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Thermostat – Fits Yamaha 2-Stroke 9.9-55 HP (Replaces 6F5-12411-01/...
Product Details
This is a high-quality aftermarket Yamaha Outboard Thermostat 143°F/62°C, designed for a wide range of Yamaha 2-stroke outboard engines from 9.9 HP to 55 HP, manufactured between 1986 and 1997. It ensures your engine's cooling system maintains the correct operating temperature for optimal performance and longevity.
It serves as a direct replacement for Yamaha OEM part numbers 6F5-12411-01-00, 6F5-12411-02-00, and 6F5-12411-03-00, as well as Sierra part 18-3625.
- Regulates engine temperature at 143°F (62°C).
- Direct-fit installation into the thermostat housing.
- Comes with a new gasket and O-ring for a complete seal.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By | Notes |
|---|---|---|---|
| Yamaha | 6F5-12411-01-00 | 6F5-12411-02-00 | Original part, now superseded. |
| Yamaha | 6F5-12411-02-00 | 6F5-12411-03-00 | Intermediate part, now superseded. |
| Yamaha | 6F5-12411-03-00 | Current OEM replacement. | |
| Sierra | 18-3625 | Aftermarket cross-reference. |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This thermostat is specifically designed for select Yamaha 2-stroke outboard models.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | 9.9, 9.9EL, 9.9ES | 9.9 | 2-Stroke | 1986–1995 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | 9.9L, 9.9S | 9.9 | 2-Stroke | 1986–1990 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | 9.9M | 9.9 | 2-Stroke | 1991–1995 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | 15, 15EL, 15ES | 15 | 2-Stroke | 1986–1995 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | 15L, 15S | 15 | 2-Stroke | 1986–1990 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | C25EL | 25 | 2-Stroke | 1991–1997 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | C25ML | 25 | 2-Stroke | 1993–1997 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | C25MS | 25 | 2-Stroke | 1992–1997 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | CV25EL, CV25EM | 25 | 2-Stroke | 1990 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | C30EL | 30 | 2-Stroke | 1991–1992 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | CV30EL | 30 | 2-Stroke | 1989–1990 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | C40EL | 40 | 2-Stroke | 1991–1997 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | C40MS, C40PL | 40 | 2-Stroke | 1992–1997 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | C40ML | 40 | 2-Stroke | 1994–1995 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | CV40EL | 40 | 2-Stroke | 1990 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | C55EL | 55 | 2-Stroke | 1991–1995 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
| Yamaha | CV55EL | 55 | 2-Stroke | 1989 | 6F5-12411-03-00 | Supersedes 6F5-12411-01-00, 6F5-12411-02-00 |
Technical Specs
- Product Type
- Marine Outboard Thermostat
- Installation
- Direct fit into thermostat housing
- Fuel Type
- Gasoline
- Operating Temperature
- 143°F (62°C)
- Other Technical Attributes
- Part of engine cooling system
What’s in the Box
- 1 x 62°C / 143°F Outboard Thermostat (6F5-12411-03-00)
- 1 x O-ring
- 1 x Gasket (682-12414-A1)
Installation Notes
- Ensure the engine is completely cool before beginning. Disconnect the battery for safety.
- Locate the thermostat housing on the engine block. Place a drain pan underneath to catch any coolant.
- Carefully remove the housing cover bolts and lift the cover off. Note the orientation of the old thermostat.
- Remove the old thermostat, gasket, and O-ring. Clean the mating surfaces of the housing and cover thoroughly.
- Install the new thermostat in the correct orientation. Fit the new gasket and O-ring in place.
- Reinstall the housing cover and tighten the bolts to the manufacturer's specified torque in a crisscross pattern.
- Reconnect the battery, top off coolant if necessary, and run the engine while checking for leaks.
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 see a high reading on your temperature gauge or receive an alarm. An uneven or weak water stream from the tell-tale can also be an indicator.
Is 143°F the correct temperature for my engine?
This 143°F (62°C) thermostat is the specified part for the Yamaha models listed in the compatibility table. While some sources may mention 140°F, 143°F is the widely confirmed OEM-specified temperature for these applications, ensuring proper engine performance and fuel efficiency.
Can I install this myself?
Yes, replacing a thermostat is a common maintenance task for those with basic mechanical skills and tools. However, always follow your engine's service manual. If you are unsure, we recommend professional installation to prevent leaks or damage.
How often should I replace my outboard thermostat?
It is good practice to inspect your thermostat annually and replace it every 2-3 years as part of preventative maintenance, especially if operating in saltwater. A faulty thermostat can lead to significant engine damage.
Is this part compatible with 4-stroke models?
No, this thermostat is specifically for the 2-stroke Yamaha models listed. Using it in a 4-stroke engine could cause improper operating temperatures and potential engine damage. Always verify compatibility.
What is the difference between this and the OEM part?
This is an aftermarket replacement, not an original Yamaha part. It is engineered to meet or exceed OEM specifications for fit, form, and function, using comparable materials. It offers a cost-effective solution without sacrificing quality or performance.
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.
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