Sierra 18-3541 Thermostat, 140F/60C, Yamaha Outboard, Replaces 66M-12411-01-00

The Sierra 18-3541 is a replacement cooling system thermostat engineered for Yamaha outboard engines. It regulates engine operating temperature by opening at a factory-calibrated 140 degrees F (60 degrees C), allowing coolant to circulate once the engine reaches proper operating temperature and helping prevent both overheating and prolonged cold-running operation. The thermostat is finished in white and is built to Sierra's quality standard, which the company states meets or exceeds the original equipment part it replaces.

This is a direct-fit cooling system component intended for outboard owners performing routine maintenance or replacing a failed or stuck thermostat. Installing a properly rated thermostat is important for outboard longevity, since running without one or with an incorrect temperature rating can cause the engine to run too cool or too hot. The 18-3541 corresponds to the OEM Yamaha thermostat 66M-12411-01-00 used in Yamaha outboard cooling systems.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3541
• Product Type: Thermostat
• Temperature Rating: 140 degrees F / 60 degrees C
• Color: White
• Weight: 0.07 pounds
• OEM Cross Reference: 66M-12411-01-00
• Application: Yamaha outboard engines

Fitment

Designed for Yamaha outboard engine cooling systems using the 66M-12411-01-00 thermostat.

Replaces (OEM)

• 66M-12411-01-00

Frequently Asked Questions

What temperature does the Sierra 18-3541 thermostat open at? It opens at 140 degrees F (60 degrees C), which is the calibrated rating for the Sierra 18-3541 thermostat.

What OEM part number does the 18-3541 replace? The Sierra 18-3541 corresponds to Yamaha OEM thermostat 66M-12411-01-00.

Is the Sierra 18-3541 an OEM or aftermarket part? It is an aftermarket replacement thermostat that Sierra states meets or exceeds the original equipment part it replaces.

What engines is the 18-3541 thermostat used on? The 18-3541 is used in Yamaha outboard engine cooling systems.

What color is the Sierra 18-3541 thermostat? It is white.

How much does the 18-3541 thermostat weigh? The Sierra 18-3541 thermostat weighs 0.07 pounds.

Does the 18-3541 come with a gasket? The Sierra 18-3541 listing covers the thermostat itself; check your engine's gasket part separately when ordering.

What happens if I install a thermostat with the wrong temperature rating? Using a thermostat rated differently than 140 degrees F (60 degrees C) can cause a Yamaha outboard to run too cool or too hot, so the 18-3541 should match this rating for proper cooling system operation.

Is Sierra 18-3541 covered under warranty? Yes, the Sierra 18-3541 thermostat is covered under Sierra's standard limited warranty.

How do I know if my thermostat needs replacing? Signs include an outboard engine that overheats, runs too cool, or shows inconsistent temperature gauge readings; a stuck or failed unit is commonly replaced with a direct-fit part like the Sierra 18-3541.

How many thermostats are included with the 18-3541? The Sierra 18-3541 includes one thermostat.