2.0 LITER GAS. 2017. Thermostat outlt bolt. A threaded rod with a drive head (such as hex, 12 point, torx, etc) on one end used to secure the Engine Coolant Outlet Housing or related components. A threaded rod with a drive head (such as hex, 12 point, torx, etc.) on one end used to secure the Engine Coolant Thermostat to it's mounting point.