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

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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.


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Fabrice

18 years of experience
133 reviews
Fabrice
18 years of experience
Toyota Yaris - Brake Pads Replacement (Front) - Orlando, Florida
My appointment was late in the day, so being late was expected. Fabrice notified me ahead of time about his tardiness. When he arrived, he was apologetic, courteous and professional. He got to work right away and let me know of other work that was needed for future appointments

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12 years of experience
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Oreste
12 years of experience
Nissan Frontier - Brake Pads Replacement (Front) - Miami, Florida
The best ever!!!! Will not use anyone else in future .. very knowledgeable and explained every thing to me .very professional, well spoken .

Breck

18 years of experience
527 reviews
Breck
18 years of experience
Jeep Patriot - Brake Pads Replacement (Front, Rear) - Houston, Texas
Becks was very informative about things that I didn't know needed to be looked at with my car. He fixed little hick ups quickly and had me ready to get back on the road sooner than I thought he would.

Miguel

19 years of experience
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Miguel
19 years of experience
Audi allroad - Brake Pads Replacement (Front) - Fair Lawn, New Jersey
Miguel is very professional mechanic. He called me in advance about his coming. He brought the quality parts (brakes pads and rotors) and done his job quickly and of great quality. I tested the brakes after the replacement and they were efficient and very silent. I would recommend him very much.

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