Fill Control/Vent System
WARNING: This page is about a different car, the 1995 Ford Windstar. However, it is still accessible from the selected car via links, so may be relevant.
Fill limiting is accomplished through configuration of fuel filler neck and/or internal vent lines within fuel filler neck and tank. Vent system is designed to permit air space in 10-12 percent of tank when tank is filled to capacity. Air space provides for thermal expansion of fuel and also aids in-tank vapor vent system.