Abstract: The invention is a cap engagable with a filler neck of a vehicle fuel tank, the cap having a core including an axially lower end, an axially upper end, and an exterior side wall extending between the axially lower and upper ends. A handle is coupled adjacent the axially upper end of the core and adapted to rotate the core about an axis of rotation between a loosened position permitting removal of the core from the filler neck and a tightened position securing the core within the filler neck. The cap further includes a seal positioned to lie around the core and a sleeve movable axially by the handle. The sleeve and has an interior side wall defining a chamber formed in the sleeve. The core lies within the chamber, and the seal lies between the sleeve and the core.