Does gasoline really go “bad” if you leave it unused for a long period of time? Some people say yes, others say no. In this article, we’ll get the advice from some experts in the field and we’ll look at some of the things you can do to make sure that older gas doesn’t damage any of the equipment you have it stored in.

Gasoline Degrades

Gasoline is a highly refined product brewed to a certain chemical composition with very specific characteristics. One primary characteristics of gas is volatility, a term used to describe how easily and under what conditions the gas vaporizes. The most highly volatile components in gasoline evaporate first. When they do, the remaining fuel’s volatility and ability to burn properly degrades. The result is diminished engine performance. Your engine may still start and run, but it probably won’t run as well as it does with fresh gas. The good news is that unless it has sat for years, all you need to do with old gas is to add some fresh gas to it and run the engine for a while. The new gas will mix thoroughly with the old gas and the combined mixture should work just fine.

A Bigger Problem: Oxidation

Hydrocarbons in the gas react with oxygen to produce gum and varnish deposits in the fuel system. These deposits and impurities can clog up gas lines and filters as well the small orifices in a carburetor and the even smaller orifices in a fuel injector. Removing these deposits can be expensive and your vehicle may not run at all or run very poorly until they are removed. The solution is to make sure that fresh gas is stored in the vehicle or device at all times.


When the outside temperatures cycle a lot, condensation can form inside your gas tank. Accord to our technical source at East Hills Chevrolet in Douglaston, NY, fuels such as E85, which have a high concentration of ethanol alcohol (up to 85%) may be even more susceptible to water contamination, as ethanol is “hydroscopic” meaning that it likes to draw moisture out of the surrounding air.You can reduce the chances of water contamination by keeping your car’s gas tank as close to full as possible, especially if the vehicle is going to be stored for an extended period.

How do you identify bad gas?

One way is to eyeball it, then smell it. Oxidized fuel tends to turn darker over time and may smell like old paint thinner. You can check stored gasoline by pouring some into a clear glass container and seeing if it looks dark.

How long does it take for gas to go bad?

That depends on a number of factors. For one, it’s hard to know how old the gas you just bought actually is. It may be fresh from the refinery, or it may be a month old already by the time you top off your tank. Some gasoline is mixed with better or more oxidation inhibitors than others.

Using a stabilizer

It’s a good rule of thumb to avoid leaving gas in your tank or a storage container for more than a couple of months. If you can’t consider using a fuel stabilizer. Using fuel system stabilizers for extended storage is far more preferable to draining the tank and leaving the system dry. This can cause rubber hoses, gaskets and seals to dry-rot and crack.


Gasoline is a highly refined substance with complex molecular bonds. Over time, these bonds break and oxidation occurs. The result is that the fuel reverts back to an earlier unusable state. The two things that you can do to mitigate this is to either add fresh gas occasionally or a gas stabilizer for long term storage.


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