Skip the auto shop - Our mechanics make house calls

Can a Loose Gas Cap Let Gas Leak Out of the Fuel Tank?

Locking Gas Cap

The short answer is: yes ... kind of.

What escapes out of a loose or faulty gas cap is gas vapor. Gas vapor rises off of the pool of gasoline in the tank and hangs around in the air. When the pressure in the tank is too great, the vapor enters the fuel vapor canister through a small outlet in the filler neck of the gas tank. In the past the vapor was just vented out of the filler cap, but that was before anyone was aware of the impact that gas vapor has on air quality.

On top of lowering air quality, lost fuel vapor adds up to a good amount of lost fuel over several years. The fuel vapor canister lets vapor released along the fuel system be sent back into the fuel tank.

How to prevent a gas cap from leaking gas vapor

The gas cap on every vehicle should have directions either on it or near it explaining how it should be used in order to properly seal the fuel tank. The most common way to ensure a good seal is to listen for clicks that the cap makes while being tightened. Three clicks is the average, but some manufacturers use caps that click once or twice.

A loose gas cap may also trigger the Check Engine Light, so if the light pops on randomly (or right after filling up), tighten the gas cap again before further diagnostics are done.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
Veteran and Military Driver Laws and Benefits in Idaho
The state of Idaho offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch in the...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...


Related questions

Q: Gas tank implodes/ won't fill.

Your fuel tank is going into a vacuum when the engine is running. The vacuum condition is causing the fuel tank to collapse and the gas cap is supposed to let in fresh air from the outside to keep the...

Q: Need a way to drain out 1 year old gasoline sitting in an otherwise good car.

Hi there. If the fuel is only a year old, then it should be fine to drive off and fill up with fresh gas as it runs out. If you really want to get the fuel out of the tank,...

Q: Bleed fuel rail pressure

Hello there, A few different faults can cause the vehicle to not start. The most common would be the battery, starter, battery cable, fuel pump, fuel filter, ignition switch wiring fault. A qualified technician such as one from YourMechanic will...