66M-12411-03 Yamaha Thermostat | Genuine OEM Yamaha Outboard Part

🔧 Product Description

Genuine Yamaha Outboard Thermostat - Part Number: 66M-12411-03

A genuine Yamaha cooling-system thermostat for selected small and mid-range four-stroke outboards.

The thermostat regulates cooling-water flow according to engine temperature. The current Yamaha service family is commonly catalogued under 66M-12411-01, with the supplied 66M-12411-03 reference belonging to the same replacement family.

⚙️ Key Features

• Genuine Yamaha OEM cooling-system thermostat
• Yamaha reference 66M-12411-03
• Current related Yamaha service reference 66M-12411-01
• Regulates engine warm-up and operating temperature
• Cross-references with Sierra, WSM and Mallory thermostats

🚤 Compatibility

Commonly used on

• Yamaha portable and mid-range four-stroke cooling systems

Typically suits

• Engine models:
• Yamaha F2.5
• Yamaha F4, F4A and F4B
• Yamaha F5A
• Yamaha F6, F6A and F6C
• Yamaha F8, F8C, F8F and T8
• Yamaha F9.9, F9.9F, F9.9J and T9.9
• Yamaha F15A, F15C, F15E, F15L and F15S
• Yamaha F20A and F20B
• Yamaha F25 and T25
• Yamaha F30
• Yamaha F40 and F40A
• Yamaha F50 and T50
• Yamaha F60 and T60
• Yamaha F70
• Yamaha F80
• Yamaha F100 four-stroke applications using the 66M thermostat family
• HP Range: 2.5HP - 100HP
• Engine Type: Yamaha four-stroke outboard
• Year Range: Approximately 1998 onward, dependent on cooling-system diagram

🔌 Function

The thermostat restricts cooling flow while the engine warms and opens as operating temperature rises. This maintains correct combustion temperature while preventing overheating.

⚠️ Common Signs of Failure

• Engine overheats because the thermostat remains closed
• Engine runs excessively cold because the thermostat remains open
• Poor idle quality or excessive fuel use during warm-up
• Corrosion or salt deposits restrict thermostat movement
• Engine temperature becomes unstable during operation

🔄 Supersession & Cross Reference

OEM Supersession Chain

• 66M-12411-01 → Supersedes 66M-12411-00
• 66M-12411-00 → Supersedes 6G8-12411-03
• 6G8-12411-03 → Supersedes 6G8-12411-02
• 6G8-12411-02 → Supersedes 6G8-12411-01
• 6G8-12411-01 → Supersedes 6G8-12411-00
• 66M-12411-03 related Yamaha thermostat service reference

OEM / Related Numbers

• 66M-12411-03
• 66M-12411-03-00
• 66M-12411-01
• 66M-12411-00
• 6G8-12411-03
• 6G8-12411-02
• 6G8-12411-01
• 6G8-12411-00
• 6AH-12411-00

Aftermarket / Verified Equivalents

• Sierra: 18-3541
• WSM: 775-205
• Mallory: 9-43037
• EMP: 75-75506
• Aftermarket reference: 13012

📦 Condition

• Genuine Yamaha part
• Brand new
• Supplied in original or equivalent packaging