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How Do You Treat Old Gas in a Lawn Mower?

By Jeff Mercer · Updated September 24, 2026 · 3 min read
How Do You Treat Old Gas in a Lawn Mower?
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Hey there, it’s your pal Jeff here. I’ve got a funny story for you about old gas and lawn mowers. So, I was mowing my lawn the other day and I ran out of gas.

No big deal, right? I just went to the garage, grabbed a can of gas, and filled ‘er up. But here’s the thing – I didn’t realize that the gas in that can had been sitting in there for like, a year. And let me tell you, it was not a good time.

What Happens When You Use Old Gas in a Lawn Mower?

Long story short, my lawn mower sputtered and died within minutes of me using that old gas. And it wasn’t just because I was out of gas – it was because the gas had gone bad.

You see, over time, gasoline starts to break down and form all kinds of nasty stuff, like varnish and gum. And when that gunk gets into your lawn mower’s engine, it can cause all kinds of problems.

How Do You Treat Old Gas in a Lawn Mower?

So, how do you treat old gas in a lawn mower? The first step is to identify if you’ve got old gas in your tank.

If you haven’t used your lawn mower in a while and you’re not sure how old the gas is, you can try the “sniff test” or the “float test” to see if the gas has gone bad. If the gas has started to break down, it’s best to drain it out of the tank and refill it with fresh, high-quality gas.

If you want to try and salvage the old gas, you can try adding a fuel stabilizer to it. Fuel stabilizers are chemicals that help extend the shelf life of gasoline by inhibiting the breakdown process.

However, keep in mind that fuel stabilizers are not a cure-all – they can only do so much to extend the life of old gas. If the gas is really old (like, over a year or so), it’s probably best to just ditch it and start fresh.

FAQ

Can You Treat Old Gas in a Lawn Mower?

You can try to treat old gas in a lawn mower by adding a fuel stabilizer to it. Fuel stabilizers are chemicals that help extend the shelf life of gasoline by inhibiting the breakdown process.

However, keep in mind that fuel stabilizers are not a cure-all – they can only do so much to extend the life of old gas. If the gas is really old (like, over a year or so), it’s probably best to just ditch it and start fresh.

Can Old Gas Damage a Lawn Mower?

Yes, old gas can definitely damage a lawn mower (or any other gas-powered equipment). When gasoline starts to break down, it can form all kinds of gunk that can clog up the engine and cause serious problems.

If you’ve got old gas in your lawn mower and you’re not sure if it’s still good, it’s best to drain it out of the tank and refill it with fresh, high-quality gas.

How Do You Store Gas for a Lawn Mower?

If you want to store gas for your lawn mower (or any other gas-powered equipment), here are a few tips:

Store the gas in a clean, approved container.
Keep the container in a cool, dry place.
Make sure the container is sealed tightly to prevent air from getting in.
Add a fuel stabilizer to the gas to help extend its shelf life.

Conclusion: Don’t Let Your Gas Go Stale

In conclusion, it’s important to keep an eye on the age of the gas in your lawn mower (and other gas-powered equipment).

Old gas can cause all kinds of problems, and it’s generally best to drain it out of the tank and refill it with fresh, high-quality gas. If you need to store gas for a while, make sure to follow the tips above to help extend its shelf life.

So go out there and give your lawn the cut it deserves, my grass-cutting friend! Just make sure you’ve got some fresh gas in the tank first.

Before you start the repairI'm a homeowner who does his own small-engine work, not a certified technician. Before any repair, pull the spark plug wire and let the engine cool. Anything involving blades under a raised machine, fuel system leaks or transmission internals — if you're not sure, have a dealer or small-engine shop look at it.
Jeff Mercer

Written by

Jeff Mercer

Hi, I'm Jeff. I look after about an acre of lawn, a riding mower, a zero-turn, a push mower that is older than some of my neighbours' cars, and a snowblower that only ever breaks the night before a storm. Doing my own repairs started as a way to save on dealer labour and turned into the part of yard work I actually enjoy.

GardenTooly is where I answer the questions people type into a search bar while standing next to a machine that won't behave: why the deck shakes, why the mower dies when it warms up, whether a bent blade shaft can be straightened, what the difference between two transmissions really means for you, and which fuel additive is worth the shelf space.

I'm not a certified small-engine technician and I don't sell equipment. Where I've done a job myself, I say so. Where an answer comes from the owner's manual, a service bulletin or a mechanic who knows more than me, I say that instead — and anything involving blades, fuel, jacked-up machines or a hydrostatic transmission gets a plain "take it to a shop" when that's the right call.