How Long Can Gas Sit in a Car Before it Goes Bad?

Jessica Shea Choksey | Aug 25, 2020

Since the start of the global health crisis earlier this year, the number of miles driven daily by car owners has dropped off sharply.

How long can gas in a car stay good

For many, their daily commute to the office has been eliminated altogether. Furthermore, road trips to see friends and family members have seen a drastic reduction. In short, this means there are cars sitting in driveways for longer periods of time than ever without being driven. 

So, what happens to the gasoline inside these vehicles when it stagnates for weeks or even months? How long can gas sit in a car before it goes bad?

The Shelf Life of Fuel

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, 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 just 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.

Identifying Bad Fuel

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.

You can also try a fuel stabilizer, which is an additive that will combat fuel breakdown. It is mixed into a full tank of gas to help make it last longer. This is a good option for many people who are driving less these days.

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.

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