Yamaha - Thermostat Engine Cooling 6AW-12411-00-00. Overview. On large Yamaha offshore motors, temperature control is critical for keeping the engine running smoothly under heavy load. The Yamaha 6AW-12411-00-00 Thermostat helps regulate coolant flow so the engine warms up properly and maintains a stable operating temperature. When thermostats wear out or stick, engines can run too cold or start running hotter than they should. Replacing this part during regular cooling system service helps keep