Updated at: 26-08-2022 - By: Lucas

You should check your gas cap if you’ve been having troubles with your car recently. Fuel efficiency might be reduced and engine performance can suffer as a result of a loose gas lid.

We’ll go over some of the issues that can arise if the gas cap is loose in this article. A loose gas cap can easily be fixed with a few simple steps. Always check the gas cap if your vehicle is having problems.

What Does A Gas Cap Do?

A car’s gasoline tank is sealed with a gas cap. Because fuel can evaporate and escape from the tank if the gas cap is loose, it is critical that it be tight. A loss in fuel efficiency and emissions can result from this.

What Problems Can A Loose Gas Cap Cause?

What Problems Can A Loose Gas Cap Cause

It may not seem like a huge concern if the gas cap is loose. However, a slack or missing gas cap can lead to a wide range of issues. If the situation is ignored for too long, it will only get worse:

Losing Fuel Economy

It’s possible that the evaporative emission control system will be harmed if your gas cap is missing or loose. Your car’s engine may leak unburned fuel into the atmosphere if the filler neck is clogged. This might cause serious environmental consequences.

As a result of cold running, a loose or missing gas cap can allow dirt and moisture to enter your car’s fuel system.

If this occurs, the vehicle’s power and performance may suffer. As if that wasn’t bad enough, an air leak from the evaporative emission control system can reduce its effectiveness due to heated air.

Your car’s pricey components could be damaged and overheated as a result of this, as well as a waste of fuel.

Engine Misfires

It is possible for impurities to enter your vehicle’s gasoline tank if the gas cap is unfastened. Engine misfires can occur as a result of gasoline evaporation-induced debris and moisture.

If your car’s ignition system has too much moisture, you may notice rough idling or stopping when you try to start it.

A Loose Gas Cap Can Also Lead To More Problems With The Environment

When unburned fuel is released into the atmosphere, it doesn’t just vanish into thin air. It is possible that the hydrocarbons discharged from your gas tank will have a negative impact on the quality of the air you breathe.

You’ll Pay More for Gasoline

Gas prices go up if you’re driving about with a loose or missing gas cap. A missing or damaged gas cap might cost you as much as 11 cents per gallon in gas expenditures.

The Car’s Under-Car Gas Tank Vapor Recovery System

Gas tank vapor recovery systems can lose their suction if the gas cap is missing or loose, allowing unused vapors to be burned off instead of recycled back into the engine to minimize emissions. This is known as flaring.

Pedestrians may be at risk because of the vapors that have escaped from your vehicle.

You could cause damage to the evaporative emissions control system

The emissions control system in your car can be damaged if the gas cap is left off or loose. Your evaporative emission control system’s hoses, valves, and seals could be permanently damaged as a result of these high temperatures in the gasoline tank.

To pass an emissions test, you must ensure that these components are performing properly.

What Causes A Loose Gas Cap?

Many circumstances can lead to a loose gas cap, such as:

How to Check if your Gas Cap is Loose

What Problems Can A Loose Gas Cap Cause-2

To remove the plastic cover from the gas tank, you’ll need to crawl down on all fours, put on gloves, and get beneath the car while it’s running so you can put the gas cap back in. Using a mirror, you can inspect the vehicle’s underside if you are unable to reach below it.

Place anything reflective (like aluminum foil) on a wall so that you can see what’s going on underneath through any open spots around either side of the bumper while gently driving up to a wall.

In order to avoid carbon monoxide poisoning, be sure to turn off your car’s engine before attempting this!

Gas Cap Repairs

Tightening the gas cap just a little bit can tell mechanics and do-it-yourselfers whether or not they need a new one. You may have a vapor leak in your vehicle’s evaporative emissions system if your check engine light comes on shortly after you’ve driven away (EVAP).

Most of the time, this issue can be solved by just replacing the old or faulty gas cap. It only takes a few minutes and doesn’t cost much at all. But don’t be surprised if your mechanic does more than just replace your gas cap when he or she fixes your vehicle.

This is due to the fact that changing a broken or outdated gas cap may also entail

To detect when the system is under too much pressure, a switch attached to this hose opens and closes based on the amount of pressure in the system.

Just enough pressure is required to open and close this switch, ensuring that you receive adequate gas flow without being overwhelmed. If you apply too much pressure, you run the risk of causing a spill.

As a result, the rest of the process is aimed at preventing this from happening by ensuring that your tank is filled with just the right amount of air, but not too much.

As part of the gas cap repair procedure, your mechanic may need to replace one or more of the following components:

Repairing or replacing an outdated or malfunctioning gas cap will save you money in the long run since the EVAP system is what reduces pollution from your car.

Replacement of any of the system’s components helps ensure that it continues to operate at its best and most efficient level. It may cost less than $10 to replace the gas cap, but mechanic labor charges are often much higher, especially if he has to do more than just tighten the gas cap.

Replacement parts could soon pile up if something has be replaced for this method to work.

It’s a good idea to inspect under the hood and see if there’s anything else that needs to be serviced in addition to the gas cap replacement. For this reason, the labor cost may end up costing you less than if you had those other components done separately or not at all.

Changing a gas cap during an oil change normally takes around 20 minutes at most dealerships, but if your mechanic has to replace other parts as well, it might take considerably longer.

How To Replace Gas Cap Yourself?

What Problems Can A Loose Gas Cap Cause-3

Why not attempt it on your own?

That’s OK. In order to safely replace the gas cap on your own, you’ll need to follow a few guidelines:

The EVAP system should be fixed if there are other issues that need to be addressed, but you should also try to figure out why.

The most common fix for loose parts clanging around is to replace rubber hoses (if necessary) and tighten the gas cap, but if this doesn’t work or mechanic labor rates are prohibitively high, you may have to have your entire EVAP system replaced, which includes much more than just the gas cap.

It’s not a good idea to assume that a new item purchased from your local dealership will fit your GM car without checking the part number first, as certain models require different part numbers for replacement parts.


How Many Types Of Gas Caps Are There?

Traditional gas caps are found on most modern vehicles, however some trucks and older cars may require you to twist their gas caps open.

Unlike the twist-open type, which requires a spring-loaded locking mechanism to secure it after being twisted back on, the screw-on type seals correctly after being twisted back on.

What Types Of Gas Caps Can Be Purchased?

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A universal gas cap fits all vehicles, but a vehicle-specific cap only fits particular models due to the filler neck design or form. Both types of gas caps are available.

It’s common to find universal gas caps made of plastic or aluminum, but stainless steel and carbon fiber are also available (stronger than regular metal ones).

There are a variety of forms to choose from, such as squares, rounds, domes, teardrops, and more. In the end, it’s always advisable to choose vehicle-specific gas caps rather than universal ones.

All vehicle-specific gas caps have a similar basic design: a larger, spring-loaded cap with an external locking mechanism and a smaller internal cap connected to the filler tube inside your tank.

Take your old gas cap when shopping for a new one online or at an auto parts store because these gas caps only fit certain models (based on their filler neck dimensions).

Will All Universal Gas Caps Fit Right Away?

For the most part, when you install a universal gas cap, it will look like it’s a perfect fit but this isn’t always the case.

Some vehicle-specific ones may even appear to fit when placed side by side, but they will not lock into place. Be sure to check for this before you leave the parts store or click on any order now buttons!

Are Metal Gas Caps Better Than Plastic Ones?

This question doesn’t have a simple yes or no answer mostly because everything is relative to the type of car you drive. If your car was made during the 70s for example, then it’s entirely possible that its gas cap was made out of metal which in turn means that it would produce better mileage than newer models.

While this might seem counter intuitive for some, just remember that older cars were built using older technologies & materials both of which often came with their own disadvantages when compared to today’s standards.

Still, even by modern standards not all metal caps are created equal. They can have different base shapes (round vsrectangle), locking mechanisms (grip vslock vssnap) & sizes so take these features into account whenever buying a gas cap.

At the same time, you should always try to avoid plastic parts of any kind, especially for your car’s fuel tank filler cap.

How Often Should I Replace My Fuel Tank Filler Cap?

You can’t generalize because it is dependent on how often you drive. Most city drivers rarely venture far from home, so it may be years before their cap begins to show symptoms of wear and tear.

After 2 or 3 years, if you reside in a rural location where driving long distances is required, we recommend replacing your gas cap. Since these places require more frequent refueling than most individuals do when living in cities or suburbs, we believe this to be true of these areas.

So How Do You Select The Right Gas Cap For Your Car?

You should always bring your old gas cap with you when purchasing a new one at a car dealership (just in case). As an alternative, here are some tips on how to pick the correct sort of fuel tank filler cap for your vehicle:

Decide on what brand and model your car has and then measure its diameter (the bottom half) while keeping in mind that some gas caps have more than one number on them.

It’s also a good idea to measure the top half of the shirt if it has a logo or graphic. Before you leave the store or click the “buy now” button, make a note of all of these digits.

Decide the diameter of your car’s gas filler tube to determine which gas cap will fit, taking in mind that most gas caps don’t have this information (unless you stumble across a specific make/model) available online.

Any number of automobile websites may provide you with detailed information about your vehicle’s characteristics at any time. If you’re shopping for fuel tank caps, keep in mind that the specifications listed for other sections of your car may not be correct.

Finally, pay attention to the material and locking mechanism of the gas cap you are now utilizing.


Caps with several locking mechanisms and/or varied materials are a particular concern. Both of these aspects should be taken into consideration while purchasing auto components, whether online or in person.

Oh, And A Couple More Tips…

If you have an exterior lock on your new gasoline tank filler cap, make sure to close it before you leave the automotive store with it (some will automatically do this once closing the driver side door).

The thought of having to stop at every gas station on your way home just so that the attendant could unlock the door for you might seem like a waste of time, but image how much more tedious that would be!

Always remember that no matter how much research you do or which gas cap you purchase, your fuel tank filler cap should always be handled as a delicate piece of equipment.

Take it back to the store for a refund or replacement if you find any issues (such your car’s mileage falling) after installing it.


Fuel tank filler caps are available in a wide variety of styles and materials today. It’s a common misconception that all universal parts will fit precisely, especially if your vehicle has a unique design or does not adhere to established standards.

So, before making an online purchase, be sure to take accurate measurements and keep in mind that these caps are delicate and should only be handled with care.