Is there such thing as bad gasoline?

“If the gas has been sitting idle in a tank for more than a three months, this is long enough for it to go bad.” -Neil Hoff

Spring is here. It’s time to bring out the lawn mower, but before you power it up, have you considered that the gasoline you are about to use might be bad?

Admit it, you have been tempted to save a few bucks by using gasoline from a leftover tank in your garage or by using what is left in the machine’s tank. In both situations, this gasoline has been sitting all winter and is no longer good.

What happens if you use old gasoline?

Gasoline has a very specific chemical composition to ensure it burns properly in an engine. One of those characteristics is volatility, a fancy word to describe how easily the gas vaporizes. The volatility decreases over time, so it can’t effectively burn in your engine. What this means for you is that your lawn mower engine may start and run, but it will not run well.

If that does not sound serious enough for you to change your ways, then consider that another side effect of using bad gasoline is the development of gum and varnish deposits in your fuel system. Over time, the composition of gas can change, creating deposits and impurities that can clog up gas lines, filters and carburetors. Removing deposits is costly, and your engine will assuredly not run until these clogs are removed. Read my blog post from last month if you are interested in learning why these impurities develop more often with major temperature changes, like from winter to summer.

How can you tell if the gas is bad?

There are several ways to tell if gas has gone bad. The first is by smelling the gas. I know this sounds unpleasant, but the fact is that everyone knows what gas should smell like. If it smells sour or off, then the gas has gone bad. Another way is by pouring some of it into a clear glass and comparing the color with that of gasoline you know is fresh. If the color is obviously darker, then the gas is bad. Finally, the easiest indicator is time. If the gas has been sitting idle in a tank for more than a three months, this is long enough for it to have gone bad.

What can I do to prevent gas from going bad?

With spring newly arrived, it’s hard to think forward to the coming fall. But, if you top off your tank and mix it with a stabilizer before your store your equipment in the fall, then you won’t be faced with this dilemma come next spring. A stabilizer is not a cure-all, but it will slow down the decomposition of the gasoline and keep it fresh for about a year. Still, the best bet is to safely drain your gas tank at the end of the season.

So, before you start up your mower, use our location finder to find the nearest Cenex® branded retailer and fill up your equipment with fresh gasoline to extend the life of your engine.

-Neil Hoff, CHS Manager of Product Marketing for Refined Fuels



2 thoughts on “Is there such thing as bad gasoline?

  1. I bought gas at Cenex dealer on March 2nd and they had bad gas only on March 4th. My vehicle has had problems and I talked to the non-american speaking lady who was very rude. I just want to know if the gas was bad on March 2nd. She said the gas was only back on March 4th. I have been filling up there every saturday. Oelwein, IA is the location of the cenex dealer. She wouldn’t tell me the dates the gas was bad she wanted to see the receipt and I did and she said nope not that day. That I was a liar. How is the gas only bad for one day. My repair man said he couldn’t figure out why my car is dieing but maybe that explains it. I put some moisture removing stuff in my car in hopes that this helps my problem. Basically I want to know when the gas was bad. It’s not possible to have bad gas only for one day. Thank you, Alicia

  2. The Cenex retail site in Oelwein is a locally-owned and operated retail site. We are reviewing and taking appropriate steps to ensure that our network of Cenex brand retailers are distributing the highest quality gas. Please send send an email with your phone number to, and we’d be happy to discuss your specific situation.

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