How Long Gas Can Sit In Your Lawn Mower

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Lawn mowers are essential tools if you want your turf grass to stay healthy and lush. But like any tool, they require care and upkeep to stay in peak condition. Staying on top of that maintenance can pay dividends in the long run and ensure your lawn mower lasts as long as possible. One of the easiest maintenance mistakes to make is forgetting about the fuel sitting in the tank. If you're not going to use your machine for a while, don't leave untreated gasoline sitting in it indefinitely — as a general rule, plan to address the fuel after about 30 days.

That's right: if you don't use your mower for just a month, you need to be sure to add a stabilizer to the tank. That's because when gasoline is left in the tank, natural chemical processes cause it to oxidize, and deposits can begin to form. This can lead to carburetor blockages and problems with the engine. 

Ethanol-blended gasoline can degrade more quickly during storage, so ethanol-free fuel is generally a better choice for lawn mowers when available. If you use ethanol-blended gas, check your mower's owner's manual to confirm the maximum ethanol content recommended for your machine, and never exceed that limit. Whether the gas is ethanol-free or not, you still need to add stabilizer prior to storage.

A fuel stabilizer like STA-BIL Storage Fuel Stabilizer can help slow fuel degradation during storage. To use it, add the amount recommended on the product label to your empty tank and then top it off with the correct ratio of gasoline. After running the mower for a few minutes to circulate the treated fuel, you should be all set. With a stabilizer added, your gas can potentially sit for up to two years. This means you can store your lawn mower with fuel in it over the winter months. Of course, if you're not interested in using an additive, you can simply drain the tank.

If you forget to add a stabilizer and your gas sits in your mower longer than expected, don't just start it and hope for the best. You may need to drain the tank and clean your carburetor to clear out the build-up. You can have this done professionally if you aren't able to take care of it yourself. While a professional cleaning could easily cost $50 or more, that's still preferable to buying a new lawn mower.