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What Happens if You Run Old Gas in a Lawn Mower?

By Jeff Mercer · Updated September 24, 2026 · 3 min read
What Happens if You Run 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, six months. 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.

What Kinds of Problems Can Old Gas Cause in a Lawn Mower?

So, what kinds of problems can old gas cause in a lawn mower? Here are a few possibilities:

  1. The lawn mower may not start at all.
  2. The lawn mower may start and then sputter and die after a few minutes.
  3. The lawn mower may start and then run poorly, with a lot of stalling and hesitation.
  4. The lawn mower may suffer engine damage due to the gunk and contaminants in the old gas.

FAQ

Can You Use Old Gas in a Lawn Mower?

In general, it’s not a good idea to use old gas in a lawn mower (or any other gas-powered equipment). Old gas can cause all kinds of problems, including engine damage, poor performance, and difficulty starting.

If you’ve got old gas in your tank 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.

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

If you use old gas in a lawn mower, it’s possible that the old gas could cause problems for your engine. Old gas can clog up the engine and cause it to run poorly or even stop working altogether.

If you’ve got old gas in your tank 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. Using old gas can cause all kinds of problems, including engine damage, poor performance, and difficulty starting.

If you’ve got old gas in your tank 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.

And if you need to store gas for a while, make sure to follow the tips above to help extend its shelf life.

So the next time you go to mow your lawn, double check that gas can before you fill up.

You don’t want to end up like me, stranded in the middle of your lawn with a dead mower and a whole lot of grass to cut. Trust me, it’s not a good look.

Before you start the repairWe are not certified small-engine technicians. 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.

Written by

Jeff Mercer

Jeff Mercer writes GardenTooly's answers to 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.

Each answer starts with the cause that is most likely and cheapest to check. Where it comes from the owner's manual, a service bulletin or what owners report, it says so, and anything involving blades, fuel, a jacked-up machine or a hydrostatic transmission gets a plain "take it to a shop" when that's the right call.

A note on our names: GardenTooly is written by a small team under pen names, one name for each job, and Jeff Mercer is the name on our mower and small-engine guides. We are not certified small-engine technicians, and we don't sell equipment.