How Long Gas Can Sit In Your Lawn Mower Before It Starts Causing Problems

If you want to keep your lawn nice and neat, you'll need to keep your mower fueled up and in good shape. Following the lawn mower tune-up and maintenance best practices is helpful, but not everything needs to be done at exactly the same time. It's good to know the reasoning behind them to ensure you're following the right schedules. For example, you may know that using last season's old gas in your lawn mower is harmful, but without knowing how quickly gas goes bad you could still run into trouble. If the gas in your mower is over 30 days old, it may already be causing problems.

The exact time the fuel in your mower will start to degrade depends somewhat on the type of fuel you're using. In general, fuel starts degrading after one to two months. Depending on the type of fuel and mower, the size of your mower's tank, and how often you're using it, this could be plenty of time. You may be using fuel fast enough not to worry about it going bad until it's time to put it into storage. However, if you mow infrequently, have a small lawn or large fuel tank, or are putting your mower into storage, then the fuel could begin degrading in the tank. It may separate, lose effectiveness, and even damage your mower. Gas can also degrade before you even put it in the mower. If your gas can has been sitting in storage for more than three to six months, you may want to rethink using it in your mower.

If you're counting the days since the last time you had to refuel your mower but aren't quite sure if you've hit 30 days or not, there are a few simple ways to tell if the fuel is still good. One of the easiest ways to check is by smell. Fuel that has gone bad often has a strong, sour smell similar to varnish or paint thinner. If you're still unsure, you can also do a visual check. Open the fuel tank and look for signs of separation. Separated fuel will have a thin, watery layer on top and a thicker, sludge-like layer at the bottom. You may also notice a change in color, with old fuel being darker than fresh fuel.

If the fuel isn't bad yet, you can add a fuel stabilizer to extend its lifespan. This is a good option if you're concerned about it going bad before you use up all the fuel, or if you're about to put your lawn mower into storage. However, while you can add a fuel stabilizer to old fuel, it won't be as effective. Fuel stabilizers can't reverse time, so if the fuel is already old enough that it's causing problems for your mower, skip the stabilizer. Instead, you should drain and clean the fuel tank, then either refill it with fresh fuel or leave it empty if you're putting it into storage. This guide to cleaning your mower's gas tank will help with that.