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  • Gasoline can typically last about 3-6 months before becoming unusable.
  • Gas goes bad because of water contamination and chemical deterioration.
  • Signs that the gas has gone bad include a rough idling engine, stalling while speeding, and an illuminated check engine light. The gas could also smell sour and look darker.

Once upon a time, we could hop into our cars and go for a drive whenever we felt like doing so. It could be a quick stop by the grocery, the daily drive to work, or a road trip to visit family or friends. After all, driving is convenient and pretty fun.

Then the global health crisis forced us to stay at home and avoid contact with other people. The overall situation has improved, but our cars still spend a lot of time gathering dust in the garage or sunning themselves up front.

Unfortunately, gasoline can go bad if it goes unused for a long time. To find out more about bad fuel, including its symptoms and ways to prevent it, read on.

Does Gasoline Go Bad?

Like the car it powers, gasoline will not last forever. It breaks down over time, especially when the contents of the gas tank are exposed to the elements or contaminants make their way inside the fuel system.

blue car refueling gas
Like the car it powers, gasoline will not last forever.

Eventually, gasoline will degrade to the point when it will not combust properly. It cannot produce the energy needed by the engine to propel the vehicle. When this happens, the fuel has gone bad and should be removed immediately.

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What Makes Gas Go Bad?

There are two things that make gasoline go bad: Chemical deterioration and water contamination.

Chemical Deterioration

Gasoline is made up of all kinds of chemical compounds. Some of these compounds are lighter and more volatile. When they come into contact with air, they react to oxygen and evaporate. These compounds account for the telltale smell most people associate with gas, especially when they’re topping their car’s fuel tank off.

Once the volatile compounds have evaporated, all that’s left of gasoline is a thick substance that resembles varnish. The varnish-like residue does not burn well and can clog fuel system components, such as carburetors and fuel injectors.

Water Contamination

One of the worst things that can happen to a fuel system is for water to find its way inside. The nasty part is that water doesn’t have to enter through an open gas cap or a leak in the gas tank. Cold temperatures can cause condensation to form on the tank’s inner surface. If you live in a state with harsh winters, the water can freeze and block the gas line.

Water is also a leading cause of corrosion in the fuel system. Rusty parts won’t run as designed and can even fall apart. Rust can also clog the gas line as well, depriving your car’s engine of the fuel it needs to run properly.

How Long Does Gas Last?

Pure gasoline can take anywhere between three and six months before it starts to break down. In comparison, diesel enjoys a much longer fuel shelf life–it can last for a year thanks to its different composition.

The same cannot be said for ethanol-blended gasoline. Ethanol is made from more volatile organic materials, so it evaporates and oxidizes much faster than pure gas. Blended gas can last for three months at the most and will usually start going bad earlier.

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It should be noted that these estimated shelf lives start from the day that the refinery produced the fuel in question. After distillation, gasoline can spend anywhere between days and weeks in storage before it gets shipped out to a gas station. Once there, the fuel gets transferred to the station’s storage tank. By the time you fill up your tank at the pump, the fuel could have already spent at least a month in storage.

Symptoms of Bad Fuel

The earlier you find out that the fuel in your car’s gas tank has deteriorated, the better. If you come across any of the following, you may have bad fuel on your hands:

What Should You Do With Bad Gasoline?

Remove bad gasoline from your car’s fuel tank as soon as possible. Driving with bad gas can cause problems like damaged internal engine parts, clogged fuel lines, and corrosion. You can prevent those issues and save yourself both money and time by bringing your vehicle to an auto service center to remove the deteriorated gas.

How to Make Gas Last Longer

Here are some easy tips to make gas last longer in your car’s fuel tank:

Stick to Pure Gasoline

Use pure gasoline because it lasts much longer on its own. Avoid adding ethanol or blended gas. Ethanol-based fuel has higher volatility–it will evaporate faster and make the rest of the gas go bad as well.

Add Fuel Stabilizers

There are times you need to store your car for many months. In those cases, you want the fuel in the gas tank to last. For long-term storage, you can add a fuel stabilizer. This fuel additive slows down the chemical reactions that break down gasoline. Depending on the stabilizer, the gas can last for at least one year.

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Top off the gas tank before adding the recommended amount of stabilizer. Next, drive your car for a short period to make sure the additive goes through the whole fuel system. Then you can put your vehicle in long-term storage.

person pouring fuel stabilizer for car
For long-term storage, you can add a fuel stabilizer.

If you’d like to see more tips about preparing your car for long-term storage, we have an article that can help you keep your vehicle –and its fuel– in good condition for future use.

Always Get the Freshest Gasoline

Fresh gasoline will last longer and burn better than old or bad gas. To increase the chances of getting the freshest fuel, look for a popular gas station with lots of customers. A heavily used station is more likely to have received a new batch of fuel. If you’re not keen on waiting in a long line, find out when the station doesn’t see many customers and drop by.

Check the Gas Cap

As the gas cap gets older, it can grow loose and not seal the fuel tank properly. Inspect your car’s cap and make sure it’s tight. Fortunately, a replacement gas cap is easy to obtain.

Bad gas will always be a problem as long as your vehicle sits in place for weeks or months. Fortunately, you can take effective steps to make sure that the gas in your vehicle’s fuel tank can last until you can drive once more.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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John F

An interesting and informative article.

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