How Long Can Gas Sit In Your Lawn Mower Before It Goes Bad?

We may receive a commission on purchases made from links.

If you've worked through the pros and cons of a gas vs electric lawn mower and have decided on a gas-powered model, you probably know that there are some maintenance tasks you need to complete before packing it away for the winter. One of the most important involves the fuel tank. You might be surprised to learn that untreated gasoline can begin to degrade in as little as 30 days, especially fuel containing ethanol. This is because ethanol absorbs water, which hastens oxidation.

To prepare your lawn mower for winter storage, or if you won't be using it for a while, empty the gas tank or add a fuel stabilizer to prevent the carburetor from clogging. A product like this helps stop fuel from degrading for up to two years, depending on the brand you use. For example, the STA-BIL fuel stabilizer is designed to keep fuel fresh for up to 24 months and protect your lawn mower engine from corrosion by dispersing moisture that may have found its way into the tank or motor. It also prevents sticky gum from building up in your carburetor due to gasoline degradation.

If you know you won't use your mower for at least the next 30 days, check the owner's manual before deciding whether to drain the tank or stabilize the fuel. Leaving deteriorating gasoline in the system can contribute to deposits, hard starting, poor performance, and fuel-system problems. If you want to empty the tank, make sure that you let the engine run until it's totally dry after you siphon the gas out. This ensures there's no gasoline left to cause problems for your mower engine. You also don't want to forget to drain the oil before storage, which is one overlooked lawn mower maintenance task that many people forget.

As mentioned, the other thing you can do is add fuel stabilizer to the tank. Always follow the directions on the product, and note that you generally won't need much stabilizer. Next, start the mower and let it run for about five minutes. This moves the stabilizer through your fuel system, protecting it from damage or corrosion while your mower sits idle. A full tank may also help reduce condensation in some storage conditions, but follow your mower's manual rather than automatically filling it completely after adding the product. These steps should help ensure your gas mower runs smoothly throughout its average lifespan of about six to 10 years.