Coolant Recovery Press Container: Operation
WARNING: This page is about a different car, the 2004 Chrysler Pacifica. However, it is still accessible from the selected car via links, so may be relevant.
The coolant recovery system works with the pressure cap to use thermal expansion and contraction of the coolant to keep the coolant free of trapped air. Provides a convenient and safe method for checking coolant level and adjusting level at atmospheric pressure without removing the pressure cap. It also provides some reserve coolant to cover deaeration, evaporation, or boiling losses.