Does Lawn Mower Gasoline Expire?

June 3, 2019

As a lawn mower repair service, one of the questions we most frequently hear from our customers is whether or not the gasoline they have sitting around for their lawn mower will ever expire.

The short answer is yes—your gasoline does expire, and it will actually expire in less time than you might expect. As a general rule, you’ve only got about 30 to 60 days after you’ve pumped the gas at your local gas station before it can no longer be used. Once it’s expired, it could do some damage to your equipment.

So why does gasoline expire, and what effects can you expect expired gasoline to have on your lawn mower? Here’s some information from a company performing lawn mower inspections in Ogden, UT.

Don’t work with expired gasoline!

Gasoline expires much faster now than it did about 10 years ago, and this is due to the larger amount of ethanol now found in fuel. The EPA mandated greater use of ethanol (an alcohol type derived from corn) in the mid-2000s in an effort to create a more environmentally friendly fuel. These days, ethanol accounts for about 10 percent of your standard 87 octane gasoline. This was both more environmentally friendly and cost effective.

However, while it’s been a good thing for the oil and gas industry as a whole, it hasn’t been particularly great for small engines, which need to be refilled more frequently and thus tend to require people to store tanks of gas on their properties. Ethanol sucks moisture out of the air over time, which results in it essentially watering down gasoline when it’s just sitting in storage. This results in negative effects on home equipment like lawn mowers and snow blowers.

As a result, with older gasoline, you might have problems getting your mower to start up. It might also fail to run as smoothly as it once did, or could have issues with sputtering or dying during its operation.

This is one of the reasons why you should never let old gasoline sit in a mower over the winter—these problems will surely manifest themselves after the gasoline has been sitting for several months. Therefore, if you have old gasoline in your mower, you will need to remove it with a siphon. If you have any built-up residue, this could choke the engine. Depending on the scope of the problem you’re dealing with and how much of that residue was present in your gas, you might have to take off the carburetor and thoroughly clean it as well before you’re able to use the mower again.

All of this means you should be smart with how much gasoline you purchase for your mower at one time. Know how much gas your tank holds, and about how much gas you use each time you mow the lawn. If you’re only mowing once a week or so, you’re not going to want to get any more gasoline beyond enough for three or four mows.

For more information, or if you’re having issues with your mower, contact Ogden Lawn & Garden to arrange for a lawn mower inspection in Ogden, UT.

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