Though this may seem like an obvious answer, there are a few things to consider to be certain that your gas cap performs at its best and no additional system damage occurs when installing your fuel cap. Ensuring your gas cap is secure and sealed is critical to your vehicle’s EVAP system performance, and knowing how to install and tighten your gas cap can also help you save money and maintain your fuel mileage. Once you’re done pumping gas or are ready to install the fuel cap, insert your gas cap into the fuel tank opening. Once your cap is in, twist it clockwise until you hear a few ‘clicks’. The right gas cap is designed to fit your vehicle and should fit the fuel tank opening easily. However, it’s important not to over-tighten your gas cap once you hear about three clicks, since in some cases over-tightening can damage the fuel filler neck. Most modern gas caps are designed to only tighten to a set tension, but this is good practice to avoid other problems. If you’re installing a replacement tethered gas cap, it’s also important to be certain that the tether is connected securely to avoid losing the cap the next time you fill up.
Gas caps are plastic screw- or twist-on caps that help seal your fuel tank. Older vehicles may have also had metal gas caps that included a seal to prevent fuel vapors from escaping the tank, while some newer models may have spring-loaded capless fuel doors that eliminate the need for a gas cap entirely. The purpose of your gas cap is to prevent liquid fuel or fuel vapors from traveling up the fuel filler neck and out of the system through the fuel door. This not only helps limit fuel evaporation that can contribute to poor gas mileage, but also reduces the risk of vapors from the gas tank polluting the air. Despite the fact that liquid fuel is not likely to come out of the fuel filler neck, a fuel cap can also help prevent gas from exiting a very full fuel tank during sharp turns, steep grades, or unforeseen events like an accident or rollover.
Although they perform a seemingly small task, your gas cap is an important component when it comes to properly sealing your fuel system, and without one, you could experience a variety of issues.
What Problems Can A Leaky Gas Cap Cause?
A leaking gas cap can increase emissions and lower fuel economy by releasing vapors from the gas tank into the outside air. Environmental conditions can cause fuel to evaporate, which can be caused by high temperatures and extreme climates. This can result in fuel vapors escaping the tank, ultimately leaving you with less fuel for your engine. Since your gas cap helps seal your fuel tank and prevents fuel from leaking, a missing fuel cap can cause performance issues and impact your gas mileage, which can make driving your vehicle more expensive.
Beyond the immediate concern of fuel evaporation, your gas cap also seals your evaporative emissions, or EVAP, system. The EVAP system on your vehicle is responsible for managing fuel vapors within the fuel system and the engine, and utilizes fuel send and return lines, a charcoal canister, canister purge valve, and finally the gas cap to prevent pollution and minimize emissions. When fuel vapors build up in the system, they can eventually be purged and burned off in the engine to minimize fuel waste. Sensors located in the gas tank of many vehicles also monitor system pressure and ensure the EVAP system remains sealed.
If you have a gas cap that is leaking or not screwed on completely, the fuel tank EVAP sensor may trigger your Check Engine light. Though these evaporative emissions codes could point to a variety of places where fuel vapor may be leaking, the most common cause of trouble codes related to the EVAP system is a fuel cap that is loose, missing, or leaking, or a leaking fuel door in capless fuel systems.
Symptoms Of A Failing Gas Cap
Though a loose gas cap can cause your Check Engine light to turn on, there may be other symptoms that are less noticeable or alarming than a warning light. You may also notice that you smell gas near the rear of your vehicle after driving even short distances, as heat and movement of the fuel in the tank while the car is in motion can cause some degree of evaporation. If you notice that your fuel cap is loose, or if you can smell gas from the rear of your vehicle, it is usually best to avoid driving as much as possible until you can inspect the fuel system or find a new fuel cap. If you have lost your gas cap entirely and aren’t able to replace it quickly, you run the risk of dirt and debris getting into your fuel system. Driving without a gas cap could cause clogged fuel filters or a damaged fuel pump, or you may notice a rough idle or unusually low fuel economy if your fuel cap is missing.
What Happens If I Lost My Gas Cap?
If you have lost your gas cap, a temporary, short-term solution may be to use a rag to cover the fuel tank filler neck opening until you can get a replacement gas cap. It’s important to note that this option is only a last resort, and that you should drive immediately to your closest auto parts supplier for a replacement gas cap, or park the vehicle until you can find a new gas cap. You run a risk of fuel vapor igniting if your gas cap is not in place, so be sure to deal with this issue immediately to minimize the possibility of injury or damage to your vehicle.
How Do I Install My Gas Cap?
Help! My Locking Gas Cap Is Stuck
Suppose you have a locking gas cap and it has failed, which means it has likely an internal mechanical issue that prevents it from being removed. This may present as a gas cap that seems to spin but never loosens, or one that makes noise when trying to unscrew it. In some circumstances with locking or non-locking gas caps, the locking cam or torque mechanism inside the cap can wear out. This can prevent the gas cap from being easily removed and leave it stuck in your vehicle.
- If you have lost the key to your gas cap or your torque-style gas cap is stuck, there are a few methods that may allow you to remove it instead of calling a locksmith or taking your vehicle to the shop.
- The first option to free a stuck gas cap is to use your hands while you try to press down with substantial force and try moving the cap yourself. This can help worn parts inside of the cap make contact, even temporarily, and this may be enough to get your gas cap unstuck.
- If your gas cap is still stuck, one idea is to slightly turn the gas cap counterclockwise, and then clockwise as if you are opening a child-proof bottle, allowing the cap to move and reset.
- Try pushing a flathead screwdriver into the gas cap lock and turning as you normally would with your key. If your own force isn’t enough and you feel confident you won’t damage your locking mechanism, tapping the screwdriver with a hammer can provide enough force to unlock the gas cap or disengage the lock.
- If you need to break the gas cap in a fuel emergency, grab a pair of locking pliers and try turning it counterclockwise with force. In some cases, you can break off the tabs that secure the cap to your vehicle’s fuel filler neck. This is not recommended due to the possibility of metal shards entering your fuel tank, and should be followed by a fuel tank flush if parts of your gas cap have been damaged near an open fuel filler neck.
If you’ve attempted all of the above methods with no success, you may have a damaged gasket that is stuck between the fuel filler housing and the gas cap itself, or the gas cap threads might have bonded to the filler housing. These issues, along with added heat from your vehicle, can make it extremely difficult to remove. Unfortunately, it may be best to bring your vehicle to a shop if you cannot remove your gas cap. O'Reilly Auto Parts® can recommend a local shop that can help you get your gas cap removed and replaced with a non-locking unit if desired.
Whether you’re switching to a locking gas cap, or if you need a replacement flex fuel gas cap or a diesel gas cap, it’s important to choose the best gas cap for your car. Discover the right fuel tank accessories, gas caps, and more to help your vehicle perform its best, reduce emissions, and keep your fuel where it should be. Find the right fuel cap for your vehicle at O’Reilly Auto Parts, where we stock diesel fuel caps, fuel cap tether clips, tethered fuel caps, vented gas caps, fuel sender units, anti-siphon tubes, and much more.