Can You Drive Without a Gas Cap?

If your gas cap warning light comes on, it could mean one of a handful of things. If you’re lucky, you’ll only need to screw it on tighter. If you’re not, it’s because it’s missing — likely it got left behind the last time you filled your tank.

If it’s the latter, you may be left wondering, can I keep driving without a gas cap? Well, maybe. On some cars, the check engine light will come on instead. There's a chance this will trigger your car to go into "limp-home mode," where it'll drive only in lower gears, at a slower speed.

That's bad. The good news is that fuel won't come spilling out of your tank. That’s because there’s a flapper valve built into your car that stops it from splashing out. So, there’s no big fire risk.

But the gas cap exists for a reason. Even if you avoid limp-home mode, over time, other problems will crop up.

Decreased fuel efficiency

Gas won’t gush out of your tank, but some of it will slowly evaporate. This reduces your fuel efficiency over time, and will end up costing you a little more at the pump. Plus, the evaporated gas can release harmful fumes into the environment around you, which is no benefit to anyone.

Engine contamination

The gas cap doesn’t just lock in your fuel, it also keeps dirt and debris out. Without it, contamination can build up in your engine and eventually hurt your car. You don't want something so seemingly minor to send you to the repair shop.

Failed emissions test

If you live in an area that requires emissions testing, not having a gas cap can cause your car to fail the exam automatically. Make sure to get a new one before you have your vehicle inspected.

Replacing the gas cap

Your car runs best with all its parts intact. When you can, check your owner’s manual (or do some vehicle-specific online research) to find out which fuel cap you need. Auto parts stores or online retailers should have what you need for $20 or less.

Once you’ve put the replacement on, your fuel cap warning light might still stay lit. Typically, it will turn off after you’ve driven 100 miles with the new cap on. If the light persists, consult your mechanic.