Aftermarket Thermostat 60°C/140°F for Yamaha 4-Stroke 2.5–80 HP Outboards – Replaces 66M-12411-01-00 and 66M-12411-00-00

Product Details

This aftermarket replacement thermostat opens at 60°C (140°F) and is designed for selected Yamaha 4-stroke outboard engines from 2.5 HP through 80 HP. It helps regulate engine operating temperature for dependable cooling-system performance.

This thermostat is listed as a replacement for Yamaha OEM part numbers 66M-12411-01-00 and 66M-12411-00-00. Earlier reference numbers associated with this thermostat family include 6G8-12411-00-00, 6G8-12411-01-00, 6G8-12411-02-00, and 6G8-12411-03-00.

• Direct replacement design for the original thermostat.
• Nominal opening temperature of 60°C (140°F).
• Small relief or bleed hole to support water circulation and air bleeding at idle.
• Aftermarket component; not manufactured by Yamaha.

Part Number Matrix

Use the following references when comparing the thermostat with the part installed on your engine. Verify the complete engine model and serial number before ordering.

Engine & Model Compatibility

The following Yamaha 4-stroke model families are associated with this thermostat application. Model, year, shaft configuration, and serial-number ranges can affect fitment, so compare your original part and consult the engine service information before installation.

Technical Specs

Product Type

Thermostat

Application

Selected Yamaha 4-stroke outboards, 2.5–80 HP

Installation

Direct replacement

Opening Temperature

60°C (140°F)

Housing Color

Silver/metallic

Additional Feature

Small relief or bleed hole for improved water circulation and air bleeding

Component Type

Single thermostat; gasket or O-ring is not confirmed as included

What's in the Box

• 1 × Thermostat

Gasket, O-ring, bolts, and other installation hardware are not confirmed as included unless specifically shown or stated with your order.

Installation Notes

1. Make sure the outboard is completely cool before beginning work. Follow the engine manufacturer's safety procedures and disconnect the battery where applicable.
2. Place a drain pan beneath the thermostat area and manage any water released during disassembly.
3. Locate the thermostat housing on the cylinder head or engine block according to the service manual.
4. Remove the housing-cover bolts and keep track of their positions if they differ in length.
5. Remove the old thermostat and inspect the gasket or O-ring. Replace the seal if required by the service procedure or if it is damaged.
6. Clean the housing and cover mating surfaces carefully, removing corrosion and old sealing material without damaging the surfaces.
7. Install the new thermostat in the same orientation as the original and ensure it is seated correctly.
8. Install the required gasket or O-ring, refit the cover, and tighten the bolts to the manufacturer's specified torque.
9. Restore the cooling-water supply and operate the outboard according to the manufacturer's procedure.
10. Allow the engine to warm up and check for proper water flow, leaks, and abnormal temperature indications.

Troubleshooting & FAQ

Safety & Important Information

• Verify the OEM reference number, engine model, year, shaft configuration, and serial-number range before ordering.
• Never work on a hot outboard or cooling system.
• Use the manufacturer's service information for torque values, sealing requirements, and installation orientation.
• This is an aftermarket replacement, not an OEM Yamaha component.
• Professional installation is recommended if you are not familiar with outboard cooling-system service.

About Sea Sierra

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