What would the classic look of American muscle cars be like without a fat, brushed aluminum gas cap perched high on the rear? This iconic look is popular for how it unabashedly flaunts a car's power and muscle. The design originally came from racing fuel caps on cars in the 50's and 50's. Race cars needed big fuel doors that were easy to open and shut during pit stops, and they needed to be made of metal so they would be strong enough to handle the aerodynamic stress of racing.

Today, many people like to dress up the appearance of their car or truck by adding on an aluminum-style fuel door of their own. Some of these fuel doors also offer the ability to lock, keeping you safe from would-be gas thieves in your neighbourhood. There are a few different companies out there making custom fuel doors. These doors vary in the types of materials used, and the style of door.

Putco makes an ABS chrome door cover which mimics the chrome used on the rest of the truck body, so it has a stock-replacement appearance. The door has embossed circular rivets arranged in a ring around the flat center. The cover can be installed very easily, using adhesive tape to stick the cover onto the existing fuel door. No drills or glue is needed. The Putco cover is for visual enhancement only, and doesn't affect performance practically. Another company, AVS, also manufactures a chrome fuel door cover which can attach using double-sided tape.

The Putco and AVS stick-on fuel doors can look great on your truck, and are pretty affordable, at $35-$45 each. But they're just for looks, and aren't too useful. If you've got the time and money, consider going for an AMI fuel door.

AMI offers a number of fuel door styles, made out of billet aluminum for a rugged look. Their colour options are: an all-black door; an all-aluminum door either brushed or polished; or an aluminum door surrounded by a black ring. The doors also have the option of being lockable, which can obviously be beneficial. Another company offering a similar product is Rampage, although their designs use less rivets and colour options are limited to brushed or polished aluminum. Rampage fuel doors can be ordered with locks as well.

Being able to lock your gas tank might seem like the best way to keep it safe from would-be fuel thieves, but it's important to remember that it's very easy to access a fuel tank directly from underneath the truck body. Persistent fuel thieves who aren't deterred by a lock on your fuel door might gain entry simply by drilling a hole in the bottom of your fuel tank. Replacing a fuel tank is significantly more expensive than replacing stolen gas, so make sure you have ways to avoid this problem before buying a lockable gas cap. Keeping your truck in a garage or well-lit lot should be enough to keep it safe.

Bottom line: Fuel door covers can be inexpensive, harmless fun, like the model from Putco, or a serious accessory, like AMI's locking billet aluminum door. However, from a purely utilitarian point of view, only AMI's locking fuel doors offer any real benefits beyond looks. AMI fuel filler doors can be purchased for about $85, and there's no extra charge for the locking model.