A locking fuel cap has a lock bolt which is slidably disposed in the cap handle and responsive to a key-operated lock mechanism to selectively drivingly connnect the cap handle to a ratchet ring. The ratchet ring is connected through a torque limiting drive to a threaded closure. When the fuel cap is unlocked, the lock bolt provides a positive drive in both opening and closing directions. If the fuel cap is locked, a spring finger on the lock bolt engages a pin on the lock mechanism when a predetermined torque is present at the ratchet ring during cap installation. The pin holds the lock bolt in a position preventing a drive connection with the ratchet ring thereafter when the cap is rotated in the opening direction.