# 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

• Supplied 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

  

🔄 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

  

🚤 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

  

📦 Condition

  

• Genuine Yamaha part

• Brand new

• Supplied in original or equivalent packaging

## Details

- **Price:** 95.7 AUD
- **Vendor:** Yamaha
- **Tags:** Yamaha Marine Parts | Outboard Engine Parts & Components

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 95.70 AUD | In stock |

## Images

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

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> Source: [Sawley's Auto and Marine](https://www.sawleysautoandmarine.com.au/products/66m-12411-01-66m-12411-03-thermostat)
> Updated: 2026-07-11