Diesel Engine
WARNING: This page is about a different car, the 2009 Dodge Caliber. However, it is still accessible from the selected car via links, so may be relevant.
The location of the container allows any air or vapor exceeding the pressure/vent cap rating to escape through the cap. Coolant flows through the container at all times during engine operation whether the engine is cold or at normal operating temperature. The coolant container is equipped with a pressure/vent cap. For more information. See Cooling/Engine/CAP, Radiator - Description