Thermostat (143°F/62°C) – Fits Yamaha 2-Stroke Outboard 9.9-55 HP (Replaces 6F5-12411-01, 6F5-12411-02, 6F5-12411-03)
Thermostat (143°F/62°C) – Fits Yamaha 2-Stroke Outboard 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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Thermostat (143°F/62°C) – Fits Yamaha 2-Stroke Outboard 9.9-55 HP (...
Thermostat (143°F/62°C) – Fits Yamaha 2-Stroke Outboard 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.
Product Details
This replacement Thermostat (143°F/62°C) – Fits Yamaha 2-Stroke Outboard 9.9-55 HP ensures your engine operates at the correct temperature for optimal performance and longevity. It is engineered for a wide range of Yamaha 2-Stroke models from 9.9 HP to 55 HP, specifically covering years 1986–1997 including series 9.9, 15, C25, C30, C40, C55, CV25, CV30, CV40, and CV55.
This part provides a direct interchange for Yamaha part numbers 6F5-12411-01-00, 6F5-12411-02-00, and 6F5-12411-03-00, as well as Sierra 18-3625.
- Designed for direct OEM-replacement fit.
- Regulates engine temperature to a consistent 143°F (62°C).
- Includes the necessary O-ring/gasket for a complete installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 6F5-12411-01-00, 6F5-12411-02-00, 6F5-12411-03-00 |
| Sierra | 18-3625 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. |
|---|---|---|---|---|---|
| Yamaha | 9.9 | 9.9 | 2-Stroke | 1986–1995 | 6F5-12411-01/02/03 |
| Yamaha | 9.9EL, 9.9ES | 9.9 | 2-Stroke | 1986–1995 | 6F5-12411-01/02/03 |
| Yamaha | 9.9L, 9.9S | 9.9 | 2-Stroke | 1986–1990 | 6F5-12411-01/02/03 |
| Yamaha | 9.9M | 9.9 | 2-Stroke | 1991–1995 | 6F5-12411-01/02/03 |
| Yamaha | 9.9MSHP | 9.9 | 2-Stroke | 1991 | 6F5-12411-01/02/03 |
| Yamaha | 15 | 15 | 2-Stroke | 1986–1995 | 6F5-12411-01/02/03 |
| Yamaha | 15EL, 15ES | 15 | 2-Stroke | 1986–1995 | 6F5-12411-01/02/03 |
| Yamaha | 15L, 15S | 15 | 2-Stroke | 1986–1990 | 6F5-12411-01/02/03 |
| Yamaha | 15ML, 15MS | 15 | 2-Stroke | 1991–1995 | 6F5-12411-01/02/03 |
| Yamaha | 15MLHP | 15 | 2-Stroke | 1991 | 6F5-12411-01/02/03 |
| Yamaha | C25EL | 25 | 2-Stroke | 1991–1997 | 6F5-12411-01/02/03 |
| Yamaha | C25ML | 25 | 2-Stroke | 1993–1997 | 6F5-12411-01/02/03 |
| Yamaha | C25MS | 25 | 2-Stroke | 1992–1997 | 6F5-12411-01/02/03 |
| Yamaha | CV25EL, CV25EM | 25 | 2-Stroke | 1990 | 6F5-12411-01/02/03 |
| Yamaha | C30EL | 30 | 2-Stroke | 1991–1992 | 6F5-12411-01/02/03 |
| Yamaha | CV30EL | 30 | 2-Stroke | 1989–1990 | 6F5-12411-01/02/03 |
| Yamaha | C40EL | 40 | 2-Stroke | 1991–1997 | 6F5-12411-01/02/03 |
| Yamaha | C40MS, C40PL | 40 | 2-Stroke | 1992–1997 | 6F5-12411-01/02/03 |
| Yamaha | C40ML | 40 | 2-Stroke | 1994–1995 | 6F5-12411-01/02/03 |
| Yamaha | CV40EL | 40 | 2-Stroke | 1990 | 6F5-12411-01/02/03 |
| Yamaha | C55EL | 55 | 2-Stroke | 1991–1995 | 6F5-12411-01/02/03 |
| Yamaha | C55TL | 55 | 2-Stroke | 1993–1995 | 6F5-12411-01/02/03 |
| Yamaha | CV55EL | 55 | 2-Stroke | 1989 | 6F5-12411-01/02/03 |
Technical Specs
- Product Type
- Thermostat
- Installation
- Direct OEM Replacement
- Operating Temperature
- 62°C (143°F)
- Materials
- High-grade corrosion-resistant housing and spring
- Package Contents
- Thermostat with O-ring/gasket
What’s in the Box
- 1 x Thermostat (Replaces 6F5-12411-03-00)
- 1 x O-ring/Gasket
Installation Notes
- Ensure the engine is completely cool and disconnect the battery for safety.
- Locate the thermostat housing on the engine block or cylinder head. Place a drain pan underneath.
- Carefully remove the bolts securing the housing cover. A small amount of coolant may spill.
- Note the orientation of the old thermostat before removing it. Remove the old gasket and clean both mating surfaces thoroughly.
- Install the new thermostat in the same orientation as the original. Place the new gasket onto the housing.
- Re-secure the housing cover, tightening the bolts to the manufacturer-specified torque in a crisscross pattern.
- Reconnect the battery, refill the cooling system, and run the engine while checking for leaks.
Troubleshooting & FAQ
What are the signs of a bad thermostat?
A faulty thermostat can cause the engine to overheat (if stuck closed) or run too cool (if stuck open), leading to poor performance, increased fuel consumption, and potential engine damage. An erratic temperature gauge is another common indicator.
How often should I replace my outboard's thermostat?
For preventative maintenance, it's wise to inspect and consider replacing your thermostat every 200-300 hours or every 2-3 years, especially if operating in saltwater. Always consult your engine's service manual for specific recommendations.
Is this the correct temperature rating for my engine?
This thermostat is rated for 143°F (62°C), which is the standard OEM specification for the listed Yamaha models. Using the correct temperature thermostat is critical for engine efficiency and longevity.
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.
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