Expansion Tank
WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
The expansion tank is positioned on the left in the engine bay. It is connected to the coolant pump and the upper right-hand part of the radiator. The latter connection is designed to bleed air from the cooling system. The coolant in the expansion tank does not circulate through the system.