Use of a locking gas cap protects a vehicle from gasoline theft or fuel system vandalism. A key lock prevents the cap from turning counterclockwise while it is tightly secured over the fuel port. Attempting to take off the gas cap without the key can prove to be more of struggle than a typical vandal or thief will make time for. Just be sure you have the key when you arrive at the gas pump to be able to remove a locking gas cap.
Unlock the fuel-fill access door. Some cars with electric door lock systems will secure the access door over the gas cap whenever the car is locked. Simply unlock a door on the car to open the fuel door on such models. Other makes have a lever under the dashboard or driver's seat that unlocks the fuel door.
Unlock the gas cap. Slip the key into the slot on the centre of the cap with the teeth toward the outer circle.
Turn the key clockwise. The lock cylinder gives and allows the key to move.
Turn the gas cap counterclockwise. Unscrew the cap until it's completely off the threads.
Replace the cap and tighten it. Slip the key into the slot and hold the cap by the still with one hand while turning the key counterclockwise. Remove the key and check the lock by trying to open the cap.
Locking gas caps are available for use on vehicles that are not sold with them. Check your favourite auto-parts store for a locking gas cap to fit your vehicle.