Can You Use Old Gas in Your Lawn Mower? Expert Advice for Fueling Your Lawn Mower

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The mowing season is here, and you plan to take out your mower to give your lawn the much-needed trim. And not many of us own those fancy electric mowers and still rely on our old rusty dusty gas mowers, but let’s be honest, they aren’t the most cost-effective ones as they end up using a lot of gas, and gas isn’t cheap these days!

So, in that case, it can be quite tempting to use the red can of old Gasoline kept in the corner of your garage. You have no idea how long it has been there, but it is OLD for sure.

But should you be using it, though? Will that mess up anything with your mower’s engine? That’s exactly what we are going to discuss today, so keep on reading.

Understanding The Composition of Gasoline

Before we head direct whether you should be using old Gasoline in your mower or not, let us understand the composition of Gasoline and how time affects it.

As many of us know, gasoline is a compound made of hydrocarbons, but we don’t know that it also contains some low amounts of oxygen. Apart from that, it also comprises low concentrations of sulfur, nitrogen, and metals.

Over time they oxygenate, and these low-concentration elements get exposed to air’s oxygen and get into an oxidation process, forming contaminants; on the other hand, the hydrocarbons get evaporated, which are the combustible parts. Hence you get left with fewer hydrocarbons and more heavy contaminants that are non-combustible.

You can easily find out if your Gasoline has been exposed long enough to the point of instability, as the oxidation reaction also causes gum formation. Gum is the goopy residual that gets piled up on the insides of a gasoline tank or engine.

Now you may think about the duration after which you can declare Gasoline as “old.” You’ll be surprised to know that it can be as little as two months. Experts say that after two months of getting exposed to air and oxidation, no one can guarantee that it would match the specifications for engine use.

Effects of Old Gasoline on Lawn Mower Engines

Now that you know how the quality of Gasoline deteriorates over time, let us discuss the effects old Gasoline can have on your mower engine.

1. Poor Performance

Poor Performance

Old Gasoline can lose its volatility over time. This means it may not ignite as easily or burn as cleanly as fresh Gasoline. This can lead to poor engine performance, including difficulty starting the engine, rough idling, stalling, and decreased power or efficiency.

2. Engine Damage

Old Gasoline can form gummy deposits or varnish-like coatings on various parts of the engine, including the carburetor, fuel lines, and fuel injectors. These deposits can clog these components, leading to engine damage or failure.

3. Corrosion


If the Gasoline has absorbed moisture over time (which can happen if it’s been stored improperly or for a long time), it can lead to corrosion in the fuel system. This can cause further damage to the engine.

4. Chemical Reactions

Many types of Gasoline contain ethanol, which can attract and absorb water from the air. Over time, this can lead to phase separation, where the water and ethanol separate from the Gasoline and sink to the bottom of the fuel container. If this mixture is used in an engine, it can cause significant damage.

Steps to Determine Gasoline Quality

Steps to Determine Gasoline Quality

Now most of us store Gasoline in our garage in those red tanks, and usually, they are airtight, making it less likely for the gas to get exposed to air; however, if you keep the knob loose, then it might not work great.

So how to know if the gas is still good to use or not? Well, you can do a little test at home without much equipment to check that. All you need is a filter paper.

Take the filter paper and put a droplet of Gasoline on it. The gasoline should evaporate completely within two minutes or so and should leave no stain. But on the contrary, if you see some yellow or brown stains on the filter paper, the petrol is adulterated.

Precautions For Using Old Gasoline

Using old Gasoline in your mower can potentially cause problems, as Gasoline can degrade over time. If you must use old Gasoline, here are some precautions you should take

1. Check The Condition of Your Gasoline

Check The Condition of Your Gasoline

If the Gasoline has been properly stored in a sealed container and out of direct sunlight, it might still be usable. However, if it has a sour smell, appears cloudy, or has visible debris or water in it, it’s best not to use it. Or you can use the test I have mentioned above to check its purity.

2. Use a Fuel Stabilizer

If the Gasoline is only a few months old, you might be able to rejuvenate it with a fuel stabilizer. This product can help restore lost gasoline potency.

3. Mix Old Gasoline With a Fresh One

Mix old Gasoline with a fresh one

If the old Gasoline isn’t too degraded, you can mix it with fresh Gasoline. A good ratio is 1 part old Gasoline to 5 parts new Gasoline.

4. Clean The Engine Carburetor

Old Gasoline can leave deposits in the carburetor and fuel lines of your mower. If you’re going to use old Gasoline, be prepared to clean these parts.

5. Use a Fuel Filter

Use a Fuel Filter 

A fuel filter can help catch any debris or impurities in the old Gasoline before it enters your mower’s engine.

Best Ways For Gasoline Storage

Once Gasoline goes bad, there’s very little room for you to make use of it and not just throw away your money. So if you don’t want that to happen, you must store it properly. So here are some tips you should keep in mind while storing Gasoline for the next time.

1. Use an Approved Container

Use an Approved Container

Always use containers that are approved for gasoline storage. These containers are designed to hold Gasoline safely and prevent leaks. They are typically made of metal or high-density polyethylene plastic.

2. Keep it in a Cool And Dry Place

You should always store Gasoline in a cool, dry place away from direct sunlight since high temperatures can cause Gasoline to expand and potentially rupture the container.

3. Keep it Away From Moisture And Humidity

Keep it Away From Moisture And Humidity

Water can contaminate Gasoline and cause it to degrade faster. Make sure the storage area is dry and the container is sealed tightly.

4. Use an Air-Tight Container

Oxygen can degrade Gasoline over time. Try to fill your containers as much as possible to limit the amount of air in the container. Also, use an airtight container so that the chances of air passing through the opening is minimal.

5. Take The Help of a Fuel Stabilizer

Take The Help of a Fuel Stabilizer

If you plan to store Gasoline for more than a few months, consider using a fuel stabilizer. These additives can extend the life of Gasoline and prevent it from degrading.

6. Rotate The Stocks

Try to use your stored Gasoline within a year and replace it with fresh Gasoline. This ensures that you always have a supply of good-quality Gasoline.


Can I Mix Old And New Gas To Run My Lawn Mower?

While you can mix new gas with the old one, as the new one will compensate for the older one, you must not forget to use a fuel stabilizer.
However, it is advised not to mix Gasoline since old gas leaves behind thick residue, and the contaminants can clog up your mower. So, even though you can mix old and new gas, it will reduce the performance of your machine and can actually do more harm than good.

How To Dispose Old Gas From A Lawn Mower?

You can siphon off the gas with the help of a hose into a gas can. Also, you can disconnect the carburetor from the fuel channel and empty the gas into a container.
Since Gasoline is hazardous, it is advised to take safety measures when disposing of it.

What Is The Best Thing To Add To Old Gas In A Lawn Mower?

Once the quality of your Gasoline within the fuel tank gets old, you should get rid of it safely and refill it with new gas. However, if you still need to use it under unavoidable circumstances, always use a fuel additive or stabilizer for a smooth performance.


In short, while you might think of saving some gas money and using old Gasoline in your mower, it might result in you spending more on engine repair as old gas can damage your engine to an extent and affect the performance of your mower.

Try to avoid using gas that is more than two months old since there’s a high chance that it has gone through enough oxidation that it is left with very few combustible hydrocarbons. Still, if you really want to use it, mix it with some fresh gas so that the impurities get diluted, and the gum doesn’t get stuck to the engine.

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