Fill Up Savvy: The Dos And Don'ts Of Gas Cap Maintenance

19 December 2014
 Categories: Automotive, Blog


Your vehicle's gas cap is probably one of its simplest parts. You unscrew it to fill the gas tank and then screw it back on when you're done pumping the fuel. No big deal, right?

Your gas cap can become a big deal if its absence or poor performance causes you to fail a smog test. Just like with every other part of your vehicle, your gas cap needs a little attention from time to time. Here are some gas cap dos and don'ts:

  • Do know how to tell which side the gas cap is on. It can be embarrassing to pull up to the gas pumps only to realize your fuel port is on the wrong side. In most cars, if you look on the dashboard, there will be an arrow next to the gas pump symbol pointing in the direction of the correct fueling side.
  • Don't freak out if you lose your cap.  It is true that when the cap is off, sensors in the car will cause you to fail an emissions inspection. Your check engine light will probably also light up. Otherwise, your car is in no grave danger from being driven for a short amount of time without the cap. Fuel valves in late model cars keep gas from sloshing out. Once you replace the cap and drive 100 miles or so, the check engine light should stop alerting.
  • Do replace a missing or faulty gas cap. A gas cap isn't just a seal for the fuel tank. Some modern caps have check valves and vacuum sensors installed in them. You can actually take your gas cap to a mechanic for testing if you often smell gas, if the check engine light is, on or if you have failed an emissions test. If you must replace the cap, try to get an original equipment manufacturer (OEM) part that works with your exact make and model vehicle.
  • Don't use your gas cap as a life hack. The gas cap has been lauded on the internet as a way to jimmy a gas nozzle to keep pumping gas without having to continue holding on to the nozzle itself. People in cold climates or with large gas tanks have been motivated to have a new hands-free way to fill up after rules forced the removal of nozzle trigger locks. But the use of gas caps to jam fuel nozzles is potentially dangerous and is now illegal in some places. The good news is, fuel trigger clips are being approved again for use in some states.
  • Do know if you have a flex-fuel vehicle.  Flex-fuel vehicles can run on either gasoline or a blend of 15% gas and 85% ethanol. They look just like standard vehicles except they have yellow gas caps.
  • Do learn about specialty gas caps. There are models with chains and plastic cords to keep the cap attached to the car, locking gas caps to deter fuel theft and polished designer caps featuring skulls or car logos. Truckers even have smart gas caps that track fuel amounts at every fill up, transmitting the data via Wi-Fi and preventing the siphoning of gas.

Take care of your gas cap to avoid failing an emissions test. If you suspect your gas cap may be the cause of a smog test failure, make your mechanic aware of your concerns. There may be tests they can do to help you know for sure. For more information, check out sites like