How Long Can Gas Sit In A Car Before It Goes Bad? - J.D. Power

See All Shopping GuidesHow Long Can Gas Sit In a Car Before It Goes Bad?Jessica Shea Choksey | Jul 11, 2024

From digital nomads to snowbirds dividing time between the north and south, cars are sitting in garages or driveways for longer periods than in the past. So, what happens to the gasoline inside these vehicles when it stagnates for weeks or even months? Does gasoline go bad? And if so, how long can gas sit in a car before it goes bad?

This article covers how to identify bad fuel as well as steps to keep gasoline fresh. In addition to advice on mitigating gasoline going bad in the first place, we discuss preparing vehicles for storage and the benefits of using fuel stabilizers. 

How Long Does It Take for Gas to Go Bad?

The length of time fuel will remain useable in your gas tank is dependent on the fuel type. Regular gasoline has a shelf life of three to six months, premium or high-octane fuel should last close to nine months, while diesel can last up to a year before it begins to degrade. On the other hand, organic-based Ethanol can lose its combustibility in one to three months due to oxidation and evaporation.

Tracking the age of the fuel in your tank can be a challenge. Its life begins in a refinery where it may have been stored for an indefinite period before being transported. That period could be a few days to a few weeks. Once it reaches a gas station, it is possible the fuel can again sit for an extended time depending on how busy that particular gas station is. It is possible the gas in your tank could be over a month old when it was pumped.

Does Gasoline Go Bad?

When gasoline gets old, its chemical properties change. As a result, the engine cannot process the fuel correctly. There are several indicators if the gas in your car has gone bad. The simplest is your “check engine” light. If the car is running fine and the engine has oil, this light may have been triggered by gasoline that is burning improperly. Take your vehicle to a certified mechanic or dealership to investigate.

Another key indicator that fuel has gone bad is if the car suffers from operational problems. That could mean failure to start, a hesitant ignition, a rough-sounding idle, or loss of power while driving, especially when accelerating.

The state of gasoline can also be determined by its look and smell. Bad fuel will have a darker or muddier appearance. It will also have a sour or disagreeable odor not typical of normal fuel. Some may even describe the gasoline as smelling spoiled.

In all these cases, it is necessary to remove the bad fuel from the tank. Not only because the vehicle will not operate as it should, but also because bad gasoline can cause damage to the internal engine components as well as produce a gummy residue that could create blockages in the fuel line. Bad fuel, especially gas containing Ethanol, can also draw in water vapor which can corrode the tank and fuel system. If left for a long period of time, the damage can be costly to repair.

Keeping Gas Fresh 

There are some ways to keep your fuel from going bad. The first is to consciously make time to drive your vehicle. Even if it is for a short distance a few times a week, this will keep the fuel from getting stagnant. And it will force you to fill up with fresh fuel every month or two.

Another tactic to keep fuel from degrading over time is to top-off your tank when you fill it. This will leave less room in the tank for moisture, which can cause water contamination and eventual corrosion. Also, a full tank limits the amount of oxygen in the tank which the gasoline is prone to evaporate into.

And lastly, if you are going to store excess gasoline, it should be kept in an airtight container within a cool, low-humidity, low-oxygen environment. Containers should be no more than three to five gallons in size.

Preparing Car for Storage 

When storing your vehicle for a prolonged period of time, there are a number of preemptive steps owners can take to protect and preserve the vehicle, including washing the car and changing the oil. One of the other important strategies is to fill up the gas tank, because an empty tank is more susceptible to rust due to moisture build-up. Filling the tank prevents air and water from accessing the tank and causing corrosion.

Fuel Stabilizer 

Whether storing or using the vehicle intermittently, another option is to add a fuel stabilizer. This additive fights fuel breakdown and is something you can add on your own without needing to bring the vehicle in for service. Before adding the stabilizer, ensure your vehicle is running close to empty. Then pour the recommended amount of fuel stabilizer into the gas tank. Next, fill your tank with a gasoline that does not contain ethanol. Then start the vehicle and let it run for at least five minutes so the stabilizer moves around the tank. The stabilizer should allow the gas to last longer. 

Summary

Gasoline goes bad after a period of stagnation. Depending on the type of gasoline used, it could lose its combustibility in as little as a month or last nine months to a year. To keep your vehicle running smoothly, drive it a few times a week even for shorter distances, consider adding a fuel stabilizer, and keep the fuel tank filled to avoid moisture build-up in the gas tank. Although gasoline has a shelf life, there are plenty of actions drivers can take to avoid this becoming an issue in their vehicle. 

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