Sierra Thermostat 18-3540, Replaces Yamaha 6E5-12411-30-00, Fits T60 and T9.9 Outboards

The Sierra 18-3540 is a replacement thermostat for Yamaha outboard engines, designed to regulate coolant flow so the engine reaches and holds its correct operating temperature. It opens at 122 degrees F (50 degrees C), matching the calibration of the original Yamaha thermostat it replaces. Sierra manufactures this part to meet or exceed the specification of the original equipment it is designed to replace, making it a straightforward drop-in swap during routine cooling system maintenance or when troubleshooting an overheating or slow-to-warm engine.

This thermostat is finished in white and is compatible with the Yamaha T60 and T9.9 outboard models noted below. Note that the 18-3540 will not fit the 31L engine. A gasket is not included with this thermostat and should be ordered separately to match your engine.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3540
• Product Type: Thermostat
• Temperature Rating: 122 degrees F / 50 degrees C
• Color: White
• Special Feature: Adjustable
• Weight: 0.07 pounds
• UPC: 808282230975

Fitment

• Yamaha T60 outboard (2003-06)
• Yamaha T9.9 outboard (2005-06)
• Will not fit 31L engine

Replaces (OEM)

• 6E5-12411-30-00

Frequently Asked Questions

What temperature does the Sierra 18-3540 thermostat open at? The 18-3540 opens at 122 degrees F (50 degrees C), which matches the calibration of the Yamaha original equipment thermostat it replaces.

Which Yamaha outboards fit the 18-3540 thermostat? The 18-3540 fits the Yamaha T60 outboard (2003-06) and the Yamaha T9.9 outboard (2005-06). It will not fit the 31L engine.

What OEM part number does the 18-3540 replace? This thermostat replaces Yamaha OEM part number 6E5-12411-30-00.

Is a gasket included with the 18-3540 thermostat? No, the Sierra 18-3540 is the thermostat only; a matching gasket is sold separately and should be selected to fit your specific engine.

What color is the Sierra 18-3540 thermostat? The 18-3540 has a white finish.

How much does the Sierra 18-3540 thermostat weigh? The 18-3540 thermostat weighs 0.07 pounds.

Is the Sierra 18-3540 a genuine Yamaha part or an aftermarket replacement? The 18-3540 is a Sierra-manufactured replacement thermostat engineered to meet or exceed the specification of the original Yamaha equipment it replaces, identified by OEM number 6E5-12411-30-00.

Will the 18-3540 fit a 31L Yamaha engine? No, the 18-3540 thermostat will not fit the 31L engine.

What symptoms indicate I need to replace this thermostat? An engine that overheats, runs cold, or warms up slowly can indicate a failed thermostat; the 18-3540 is designed to restore proper coolant regulation on covered Yamaha T60 and T9.9 outboards.

What is the UPC for the Sierra 18-3540 thermostat? The UPC for the Sierra 18-3540 thermostat is 808282230975.