Q: Will I Lose Gas If My Gas Cap Is Loose?

asked by on

Will I lose gas if my gas cap is loose?

If your gas cap is loose, you will not lose fuel in its liquid form. You will, however, lose fuel in its gaseous state which is called a vapor.

Gasoline absorbs heat and, if left in an open container, will convert from a liquid into a vapor. The fuel vapor escapes into the atmosphere where it mixes with combustion gases in the ozone layer that surrounds our planet and becomes what we know as "smog."

Fuel systems on cars are designed so that all of the fuel vapor is contained within a closed system and cannot escape into the atmosphere. This is done to reduce the amount of smog in the air.

The gas cap is a vital component of your car’s fuel system. It contains a dual-action relief valve that will relieve excess pressure in your fuel tank. It also allows atmospheric pressure into your fuel tank if an excessive vacuum develops.

Vehicles built since 1996 have an emissions monitor test that checks to see if your fuel cap is doing its job. If the leak test fails, the Powertrain Control Module (PCM) will illuminate the Check Engine light and set a diagnostic trouble code for an emissions leak. The most common cause of this is the driver failing to properly reinstall the fuel cap after filling their gas tank. Another cause is a broken rubber seal on the gas cap itself.

If you have a Check Engine Light illuminated, get in touch with a qualified technician. We’ll do our best to diagnose the cause and offer you options for the most reasonable course of repair.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Will I Lose Gas If My Gas Cap Is Loose?

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Hose leaking antifreeze

Hello. The most common coolant leak that suddenly occurs on this engine is a water pump malfunction. It will start leaking coolant and it will appear to come from near the rear of the engine. It is also possible that...

Q: What does the low fuel Warning Light mean in a 2012 Chevrolet Equinox?

The low fuel Warning Light is located on your instrument panel, next to your fuel gauge. When your vehicle is nearly out of fuel, the low fuel Warning Light will illuminate, and be accompanied by a chime. The light will...

Q: Car shuts off when the weather is hot

Hello. A bad cam position sensor will cause a Check Engine Light to come on and possibly cause a stall or no start condition for your 2000 Mercury Mystique. Cam position sensors usually develop their problems when hot, so this is likely...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
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...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.