2000 Yamaha YFM400FWA(M) Factory Service workshop Manual, Page 217Get this manual

THERMOSTAT

THERMOSTAT INSPECTION 1.Check: Thermostat Does not open at 63.565.5 (146.3149.9 F) Replace

Checking steps: Suspend the thermostat in container filled with waterSlowly heat the waterPlace thermometer in the waterWhile stirring the water, observe the thermostat and thermometer's indicated temperature

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