This Is What Happens When You Use Last Season's Gas In Your Lawn Mower

The weather is warm, the sun is shining, and you've rolled your gas-powered lawn mower out of storage to mow the lawn ... but when was the last time you filled up its fuel tank? If you've broken out your mower at the start of spring only to remember it's been sitting with last season's old fuel in its tank, you might want to think twice before powering it up. Running your mower on fuel that's been sitting stagnant for months may not be a good choice for your machine. In fact, last season's old gasoline can lead to issues such as hard starts and poor engine performance. 

Old gas that's been sitting in your lawn mower's tank (or any kind of tank or container, if you've been storing gasoline in your garage) is a problem because it breaks down over time. Gasoline starts to break down after about 30 days, so it has a pretty short lifespan. In your car, this isn't usually a problem; in your lawn mower, however, it can impact the engine's performance. And when gas breaks down, it doesn't merely dissipate into thin air. Instead, it gums up, forming a filmy, varnish-like layer of debris on key lawn mower components like the carburetor, fuel lines, and injectors. That residue can prevent your mower's engine from starting, clog the carburetor, and even potentially damage the fuel system, leaving you with a much bigger problem than an empty gas tank.

If you break out your lawn mower to discover it's sitting with just a little bit of fuel, it might be tempting to put new gasoline in and get mowing with a mostly fresh tank. Unfortunately, that's not the best idea, either; mixing old and new gasoline may "freshen" things up, but you'll still be running your lawn mower on degraded fuel, which can leave deposits behind and potentially cause rough starts or running issues. Besides, any issues caused by bad fuel might void your mower's warranty, depending on the specifics of your model. In order to avoid gasoline-related issues with your lawn mower caused by old, broken-down fuel, you should drain your mower's fuel tank completely before storing it for long periods of time. 

Now, if you're hoping to make your gas last longer, there is one alternative: add a fuel stabilizer. These additives can slow down the oxidation process, helping your fuel last for as long as 12 to 15 months. As you prepare to store your lawn mower, you can drain any leftover gasoline and fill the tank with freshly stabilized fuel. That said, it's important to remember that fresh fuel is still the best choice. Fuel stabilizer merely slows down the rate of oxidization, while new fuel will burn cleaner and easier, keeping your lawn mower operating smoothly.