Air Separator
WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The air separator is a plastic tank that aids in the removal of air from the cooling system. The air separator is located in the cavity behind the left hand headlamp. Coolant enters the air separator from an upper hose that attaches to the PIM. Coolant exits the air separator from a lower hose that attaches to the coolant pumps. A third hose, attached to the top of the air separator, allows air to escape the cooling system through the surge tank.