Unscrew the old cap, screw on the new one, and you're done

Replacing a fuel cap takes about five minutes and requires no tools. Most fuel caps twist off by hand — turn it counterclockwise until it comes loose, then throw it away. Screw the new cap on clockwise until you feel it click or seat firmly. That's the entire job. The cap sits on top of your fuel door, which is usually on the side of your car near the rear wheel.

You need to know your car's fuel cap size before you buy a replacement. Fuel caps come in a few standard sizes, and buying the wrong one means a poor fit or a cap that won't seal. The easiest way to find the right size is to look at your owner's manual, call your car's dealership with your vehicle identification number (VIN), or take a photo of your fuel door opening to an auto parts store and ask them to match it.

Key Takeaways

  • Most fuel caps unscrew by hand with a counterclockwise turn; no special tools are needed.
  • Fuel caps come in standard sizes, and you must match your car's size or the cap will not fit properly.
  • Your owner's manual or dealership can tell you the correct size for your vehicle.
  • A new fuel cap costs between $10 and $30 at any auto parts store.
  • A loose or missing fuel cap triggers a check engine light and allows fuel to evaporate.

Why your fuel cap matters

A fuel cap does two things: it seals your fuel tank so gasoline does not evaporate, and it maintains the pressure inside the tank that your fuel pump needs to work properly. A loose, cracked, or missing cap lets fuel vapors escape, which wastes gas and triggers your check engine light. Your car's emissions system depends on a tight seal.

If your check engine light came on and a mechanic told you it's the fuel cap, replacing it often clears the code. Drive for a few days after you install the new cap, and the light should turn off on its own. If it stays on, the problem is something else.

Finding the right fuel cap size

Fuel caps are not universal. The most common sizes are 1.5 inches, 1.75 inches, and 2 inches in diameter. Using the wrong size means the cap will not grip the fuel door opening, will fall off while you drive, or will not seal at all.

Check your owner's manual first — it usually lists the fuel cap size in the maintenance or specifications section. If you do not have the manual, call your car's dealership with your VIN and ask for the fuel cap size. You can also visit an auto parts store like AutoZone, O'Reilly, or NAPA with your vehicle information, and they will tell you the correct size and have it in stock.

Some newer cars have capless fuel doors that do not use a removable cap at all. If your fuel door has no cap to unscrew, your car has a built-in valve that seals automatically when you remove the fuel nozzle. You cannot replace a capless system yourself — if it fails, the repair must be done at a dealership.

How to remove the old cap

Open your fuel door by pressing the release lever inside your car, usually on the driver's side floor or dashboard. Some cars require you to push on the fuel door itself to pop it open. Once the door is open, you will see the fuel cap in the center.

Grip the cap firmly and turn it counterclockwise. Most caps require only hand strength — do not use a wrench or pliers unless the cap is stuck. If it is stuck, try wrapping a cloth around it for better grip, or spray a small amount of penetrating oil around the base and wait a few minutes. Once it loosens, finish unscrewing it by hand and set it aside.

Installing the new fuel cap

Take the new cap out of its packaging and align it with the fuel door opening. The cap should fit snugly into the opening — if it is too loose or too tight, you have the wrong size. Screw it on clockwise by hand until you feel resistance. Most fuel caps have a ratcheting mechanism that clicks or seats with a firm stop when they are tight enough. Do not force it past that point.

Close your fuel door and you are finished. There is no need to start the car or do anything else. The next time you drive, your car's computer will recognize the new cap and clear any check engine light that was caused by the old one.

Where to buy a replacement fuel cap

Auto parts stores carry fuel caps in all standard sizes. AutoZone, O'Reilly Auto Parts, NAPA, and Advance Auto Parts all stock them, and you can also order online from Amazon or eBay. Dealerships sell them too, but usually at a higher price — expect to pay $10 to $30 at an independent parts store and $20 to $40 at a dealership.

If you are not sure which size to buy, bring your car's year, make, and model to the parts store, or order online using your VIN. Most online retailers will let you enter your vehicle information and show you the correct cap before you buy.

What to do if the cap is stuck or damaged

If the cap will not unscrew by hand, spray penetrating oil like WD-40 around the base where the cap meets the fuel door. Let it soak for 10 to 15 minutes, then try again. Grip the cap with a cloth for better traction and turn slowly — sudden force can strip the threads.

If the cap is cracked or leaking, replace it when ready. A damaged cap cannot seal the fuel tank, which means fuel will evaporate and your check engine light will stay on. Do not try to repair a cracked cap with tape or glue — buy a new one.

Frequently Asked Questions

Can I drive without a fuel cap?

You can drive short distances without a cap, but your check engine light will turn on within a few miles. Fuel will evaporate from your tank, and you will waste gas. Replace the cap as soon as you can.

Do I need a special tool to remove the fuel cap?

No. A fuel cap unscrews by hand. If it is stuck, use a cloth for grip or spray penetrating oil, but do not use a wrench or pliers unless you are willing to risk stripping the threads.

What if I lose my fuel cap while driving?

Your check engine light will come on within a few miles. Buy a replacement cap that matches your car's size and install it as soon as you can. The light will turn off after a few days of driving with the new cap in place.

Is a dealership fuel cap better than an aftermarket one?

Dealership caps are original equipment and may provide to fit. Aftermarket caps from auto parts stores are cheaper and work just as well if you buy the correct size. Either one will seal your fuel tank properly.

How do I know if my fuel cap is the wrong size?

If the cap is too loose and falls off, or if it does not screw down far enough to seat properly, you have the wrong size. Take it back to the parts store and ask them to match it to your vehicle. They can usually swap it for the correct size on the spot.