Yamaha – Thermostat | Engine Cooling | 66M-12411-01-00

Overview

Keeping the engine at the right temperature is critical for small and mid-range Yamaha outboards. The Yamaha 66M-12411-01-00 Thermostat regulates coolant flow through the engine so it warms up properly and maintains stable operating temperatures while running. When a thermostat sticks open or closed, the motor can run too cold, lose efficiency, or start creeping toward overheating. Replacing the thermostat during routine cooling system service helps keep your Yamaha running smooth whether you are trolling, cruising, or running long distances.

Key Features

• Engine Temperature Regulation – Controls coolant flow to maintain the correct operating temperature during engine operation.

• OEM Yamaha Precision Fit – Manufactured to Yamaha specifications to ensure reliable operation and proper installation.

• Supports Fuel Efficiency and Performance – Helps the engine reach optimal operating temperature for smooth running.

• Ideal Preventative Maintenance Part – Often replaced during water pump service or routine cooling system inspection.

Engine & Boat Compatibility

• F2.5 - All Models
• F4 - 1999-Current
• F6 - 2003-Current
• F8 - 2003-Current
• T8 - 2003-2010
• F9.9 - 2001-Current
• T9.9 - 2005-Current
• F15 - 2005-2006
• F25 - 2005-2006
• T25 - All Models
• F30 - All Models
• F40 - All Models
• F40A - All Models
• F50 - All Models
• T50 - All Models
• F60 - All Models
• T60 - All Models
• F70 - All Models
• F80 - All Models
• F100 - Up to 2000

FAQ

Q: What are common signs a thermostat may be failing?
A: The engine may run hotter than normal, take longer to warm up, or trigger temperature warnings if the thermostat stops operating correctly.

Q: Should thermostats be replaced during water pump service?
A: Many technicians replace them at the same time since both are part of the cooling system and accessed during routine maintenance.

Q: Can saltwater cause thermostat issues?
A: Yes. Salt deposits and debris can cause the thermostat to stick if the cooling system is not flushed regularly.

Q: Will a bad thermostat affect engine performance?
A: It can. If the engine runs too cool or too hot, it may not perform efficiently and could suffer long-term wear.

Q: Is this a part most boat owners can replace themselves?
A: In many cases yes, though access varies by model. It is often handled during scheduled maintenance.

• Supersessions
  66M-12411-00-00, 6G8-12411-03-00, 6G8-12411-02-00, 6G8-12411-01-00, 6G8-12411-00-00