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

asked by on November 23, 2015

Will I lose gas if my gas cap is loose?

Check Engine Light is on Inspection $79.99 - $89.99 Get a Quote

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.

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

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

What others are asking

Gas leak under car

Hello, Spotting a major gas leak under your car is not something to be taken lightly. Gasoline is a flammable, hazardous liquid and a leak in you car is a repair that needs to be addressed immediately. There are numerous...

Water leaking into floor board.

Hello, there are many entry points for water into the cabin. Assuming all windows, doors and possible sunroof were closed, the following is what I suggest. If your vehicle is equipped with a sunroof, start there and run a garden...

Issues with coolant, afraid of blown head gasket.

If the coolant is not leaking externally then it is leaking internally into the engine cylinder. I suggest looking inside the oil cap or on dipstick to see if the oil is contaminated with coolant. The oil would look milky...

1996 Chevrolet Corvette cranks but won't start

There are a few possible causes for your concern. Your engine needs several things in order to run properly: Fuel from the fuel tank, spark from the ignition system to ignite the fuel, and pressure in the cylinders generated by...

Starting in the morning

Cold weather can effect your car in a number of ways. To start, we need to know if the engine is cranking but not starting. If the engine is not cranking, or has a slow crank on cold mornings, your...

Unknown oil leak in a 2003 Chrysler PT Cruiser

Engine oil leaks will generally get worse over time so identifying the source of the leak and repairing the leak should be carried out as soon as possible. These engine are known to develop leaks at the front engine seal...

Bad mileage & strong gas smell in dipstick/oil pan - 1996 Nissan 300ZX

Okay, so usually the answer to problems are usually hidden in the fine details. The whole reason you started noticing a problem was the gas mileage. If this was my car, I would be thinking that I have a fuel...

Transmission fluid is leaking. Cracked on the bottom of the transmission.

Hi there. Depending on where the crack is located on the bottom of the transmission will depend on whether or not you will be able to fix without replacing the transmission. For example, if the crack is in the fluid...

I replaced new fuel pump and filter and ran good for two days and now it won't start

The fuel pressure should be checked to see if the new fuel pump failed. If pressure is below 40 psi when the key is turned on then replace the fuel pump and filter. When the tank is out you should...

Related articles

How Can I Keep My Fuel System Clean?
Proper Proper maintenance of the fuel system is crucial for consistent long-term performance of a vehicle. The most easily clogged parts of the fuel system are the fuel injectors themselves. There are a number of ways this can happen: ...
How to Buy a Good Quality Exhaust Manifold
The The exhaust manifold bolts to the cylinder head of the engine and pulls exhaust gases from the individual ports; combining them into one outlet to flow back into the remainder of the exhaust system. Exhaust fumes are sneaky, and...
How Can I Keep My Fuel System Clean?
Proper Proper maintenance of the fuel system is crucial for consistent long-term performance of a vehicle. The most easily clogged parts of the fuel system are the fuel injectors themselves. There are a number of ways this can happen: ...