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How Long is Gas Good for Lawn Mower: Expert Advice

Need to know how long you can store gas for your lawn mower? With our extensive knowledge in lawn mower maintenance, we’re here to provide you with the definitive answer to your question.

How Long is Gas Good in a Lawnmower:

Gasoline can go bad within 1-3 months. Use a fuel stabilizer when storing gas to extend fuel life. Harmful gas can clog filters and damage fuel lines and carburetors. Drain old gas and add fresh fuel with a stabilizer. Consult a mechanic if engine problems persist after draining old gas.

Now that you know that gasoline cannot be stored in the fuel tank forever, you should also go through the details of why and how it goes bad after a certain period and the adverse effects bad gasoline has.

Why and How Does Gasoline Go Bad?

Gasoline can go wrong because of several chemical phenomena, e.g., evaporation or oxidation. The chances of these phenomena happening and the speed at which they proceed depend on gasoline contents. The details of how and why gas goes wrong because of these phenomena are given below.

● Evaporation:

The proper gasoline combustion in the combustion chamber of your mower’s engine depends on its chemical and physical properties. The correct proportions of its contents, weights, etc., play a vital role in combustion.

Even a slight change in these properties can adversely affect the combustion process. The evaporation of a pure substance and a mixture are different because their contents evaporate at other times and rates depending on their nature.

With over two decades of experience in the field, I can confidently say that gasoline for a lawn mower typically lasts for about 60 to 90 days under optimal conditions. However, this can vary depending on factors such as the type of gasoline and how it’s stored.

– The Process of Evaporation in a Mixture

For instance, if a mixture of two liquids, A, B, and A, were more volatile, it would evaporate first. The same things happen with gasoline that has other chemicals blended in it. The more volatile components disappear first.

The bad thing is that the mixture’s lightest components evaporate first, making gasoline heavier. As said earlier, a change in gas properties affects combustion. The more severe gasoline does not combust appropriately. This means that the engine will still run but not correctly.

● Oxidation:

Oxidation is the chemical process that occurs when chemicals react and combine with oxygen to produce new compounds called oxides. For example, rusting is a form of oxidation in the presence of moisture. Oxidation of gasoline is an even more severe issue than evaporation.

Fuel oxidation occurs as hydrocarbons in the fuel react with oxygen to produce new compounds. This makes a semi-solid called gum, creating deposits all over the fuel system and clogging filters and lines.

Gum makes the affected components malfunction, causing the mower not to run smoothly or not even start at all. Gum can also affect the carburetor very severely. Gummed-up carburetors won’t work unless fixed, and fixing them is expensive.

● Ethanol:

These days, gasoline takes much less time to expire than it did some years ago. This is because of the introduction of ethanol in the fuel. The Environment Protection Agency implemented the use of ethanol in the fuel in an attempt to make the fuel more environmentally friendly.

Ethanol is a type of alcohol that is derived from corn. Nowadays, ethanol takes up to ten percent of the 87-octane gasoline. Adding up to ten percent ethanol made fueling environmentally friendly and cost-effective but created a problem for small gasoline engines. Remember that the gasoline engine of your lawnmower is also a “small” engine.

The problem with ethanol is that it draws moisture from the air as it sits in the garage or shed tank. This moisture waters down the gasoline. An engine with this watered gasoline in its combustion chamber will not start, stutter, or die during the operation.

As a general rule, replacing the gasoline in a lawn mower at least once a month during the mowing season is a good idea. If the mower is not being used, the gasoline should be drained or stabilized.

– The Problem with Small Engines

The problem with small engines such as those in lawnmowers is that they are used only briefly after several days. After use, leftover gas stays in the tank until the subsequent use. This causes exponential growth in the chances of your gasoline reaching its expiration date.

Once the gasoline expires, it causes all sorts of problems for the components of your mower’s fuel system. Fuel lines, carburetors, and seals deteriorate. A varnish buildup caused by expired gasoline can cause tiny fuel pores to clog.

Clogging of the fuel ports will make it impossible, or at least almost impossible, to start the engine. Gasoline with ethanol can last for a maximum period of 3 months. However, we advise you to consume it before that period. Using fresh fuel is very important for the health of your machines.

● Water:

Water can build up in the tank you use for storing gas. Water buildup occurs due to condensation because of temperature changes throughout storage. Water buildup degrades the gas and makes the proper combustion of gas impossible.

Reusing Old Gas:

Although reusing old fuel is not a good practice, it can be done in some cases, but the gas must be treated first to make it less harmful. Old gas can be reconditioned through nylon and cotton cloth, adding fresh gasoline in a specific ratio.

This can make the old gasoline reusable, but reusing it is not a good practice, and we don’t recommend it. Another essential thing to remember regarding reconditioning and reusing old gas is that it can be done only for engines with carburetors and not fuel injection systems.

Furthermore, this process requires special care and can’t be done by everyone. Seek the help of a mechanic if you wish to reuse old gas by reconditioning it.

Bad Fuel: Using a Fuel Stabilizer

If you intend to store fuel in a tank for more than 30 days, you should mix it with a fuel stabilizer. Using the right fuel stabilizer and integrating it with the fuel in the correct ratio will allow your fuel to sit in a tank without the dangers of pitting and gumming for more extended periods than if no stabilizer is used.

The ratio of fuel stabilizer to gasoline depends on the stabilizer brand. For correct info in this regard, you should contact the stabilizer’s manufacturer that you intend to use. An important thing to remember is that the fuel stabilizer ratio depends on the stabilizer brand and not on the mower’s model or brand.

For example, some brands recommend an ounce of stabilizer for a gallon of gasoline, while others suggest an ounce for 2.5 gallons. Another essential thing to note is that the fuel stabilizer works only with fresh fuel. You cannot add a stabilizer to old gasoline and expect it to refresh.

Fixing a Mower Affected by Bad Gas:

If your engine isn’t starting right or causing trouble because you are using old fuel, stop immediately and siphon out the old gas. Any built-up residue in the engine needs to be removed, too.

If your engine runs for some seconds and then dies even after adding fresh fuel, the carburetor has been clogged by the thick varnish-like substance that builds up after volatile components in the fuel have evaporated. Use a carburetor cleaner to clean the carburetor, and use fresh fuel with a stabilizer added to it.

For more details on servicing your mower affected by harmful gas, consult the manufacturer or a professional mechanic.

Common mistakes include using an unapproved container, storing gasoline near a heat source, or not replacing the gasoline often enough.


Gasoline can be stored only for a specific time before it goes bad. How long can gas be stored? Well, as little as 30 days under certain conditions. Gasoline goes wrong because of additives that evaporate or oxidize, degrading the fuel. This is a condition known as gas that has deteriorated.

When this happens, it is terrible for your engine. Our advice is to always use fresh fuel, preferably with a stabilizer added to it in the correct ratio. A popular choice is Sta-Bil. This is especially important if you suspect that the gas has gone wrong. One way to check is by looking at the color. The color of fresh gasoline is clear, and any discoloration could be a sign of lousy gasoline.

When storing your mower for the winter, drain and dispose of the fuel instead of storing it with fuel in the container. Any fuel left in the mower over the winter could be lousy gas when you use it again. Cleaning your mower regularly and maintaining it properly is also essential.

  1. Isabella Larson says:

    Can I mix old gas with new gas in my lawnmower?

    • Allard Vdhooft says:

      It is not recommended to mix old gas with new gas in your lawnmower. It is better to use fresh fuel for optimal performance and to avoid potential issues.

  2. Reginald Wagner says:

    How do I know if my gasoline has gone bad?

    • Allard Vdhooft says:

      Gasoline can go bad within 3 months or up to a year with stabilizers. Ethanol blended gas goes bad faster. If it smells sour or looks bad, it’s time to replace it.

  3. Jessie Lawson says:

    I never knew that ethanol in gas could cause so many problems. Good to know!

    • Allard Vdhooft says:

      Thank you for reading! It’s important to be aware of how ethanol in gas affects your lawnmower. Remember to use fresh fuel or add a stabilizer for longer storage.

  4. Maureen Prescott says:

    What are the long-term effects of using bad gas in a lawnmower?

    • Allard Vdhooft says:

      Thank you for your question, Maureen. Bad gas in a lawnmower can lead to clogging, starting issues, and engine damage. It’s best to use fresh gas with a stabilizer to avoid long-term effects.

  5. Myrtle Ray says:

    What are the signs that my lawnmower is affected by bad gas?

    • Allard Vdhooft says:

      Gas can go bad after 3 months. Signs of bad gas in your lawnmower include rough starts, engine stalling. Best practice: use fresh fuel or add stabilizer if storing over 30 days.

  6. Dave Harvey says:

    I’m glad there are ways to recondition old gas, even though it’s not the best option. Good to know!

    • Allard Vdhooft says:

      Thank you, Dave! It’s essential to know how to safely handle old gas in lawnmowers. Fresh fuel with a stabilizer is the best option for your machines’ health.

  7. Chad Collins says:

    This post has really clarified why using stabilizers is important. Thank you for the insights!

    • Allard Vdhooft says:

      Glad the post was helpful, Chad! Remember to use stabilizers to keep your gasoline fresh for longer. Thanks for reading!

  8. Daisy Andrews says:

    I had no idea that water buildup in the gas tank could be so harmful. Thanks for the warning!

    • Allard Vdhooft says:

      Thank you, Daisy! It’s great to share important information like this to help keep everyone’s lawnmowers running smoothly. Best of luck with winterizing yours!

  9. Francisco Martinez says:

    Is there a way to test the quality of the gasoline in my lawnmower’s tank?

    • Allard Vdhooft says:

      It’s best to use fresh gasoline in your lawnmower. If gas has been sitting for a while, it’s likely bad. Toss it and start fresh to avoid engine issues.

  10. Terri Cooper says:

    After reading this, I’ll definitely be more careful about how I store gas for my lawnmower. Great tips!

    • Allard Vdhooft says:

      Thank you, Terri! Storing gasoline properly is key to maintaining your lawnmower. Remember, fresh fuel with stabilizer is the best choice. Enjoy a smooth running lawn mower!

  11. Yolanda May says:

    Can I add something to the gas tank to prevent bad gas from forming?

    • Allard Vdhooft says:

      Adding a stabilizer to your gas tank can prevent bad gas from forming. Stabilizers extend the gasoline’s shelf life and help prevent oxidation. Be sure to follow the manufacturer’s instructions for the correct ratio.

  12. Keith Turner says:

    Can I use premium gasoline for my lawnmower to make it last longer?

    • Allard Vdhooft says:

      It is not recommended to use premium gasoline in your lawnmower. It is best to use fresh fuel and add a stabilizer if you plan on storing it for an extended period.

  13. Isaiah Cox says:

    The information on the different effects of evaporation and oxidation on gas was eye-opening. Thank you!

    • Allard Vdhooft says:

      Thank you for your kind words, Isaiah! I’m glad you found the information about gas effects helpful. Happy mowing!

  14. Roberta Stephens says:

    What happens if I don’t drain the gasoline from my lawnmower before winter?

    • Allard Vdhooft says:

      It’s best to drain the gasoline from your lawnmower before winter to prevent fuel deterioration, clogging, and engine issues. Fresh fuel with a stabilizer is always the best choice.

  15. Lydia Crawford says:

    How often should I add a stabilizer to my lawnmower’s fuel?

    • Allard Vdhooft says:

      Hi Lydia, For gasoline without ethanol, a stabilizer should be added every 6 months. For ethanol-blended gasoline, add stabilizer every 3 months. Stabilizers extend shelf life to 1-3 years. Hope this helps!

  16. Mathew Wright says:

    Thanks for the detailed explanation on why gas goes bad. Very informative!

    • Allard Vdhooft says:

      Thank you, Matthew! I’m glad you found the explanation useful. Feel free to reach out if you have any more questions about gas storage for lawn mowers.

  17. Irma Caldwell says:

    Is there a difference in the storage of gas for a lawnmower and a car?

    • Allard Vdhooft says:

      Store gas for your lawnmower just like you would for your car to prevent it from going bad. It’s best to use fresh fuel with a stabilizer added for longer storage periods.

  18. Loretta Carroll says:

    I appreciate the advice on how to fix a mower affected by bad gas. Very helpful information!

    • Allard Vdhooft says:

      Thank you for reading! I’m glad the advice was helpful for your mower. Remember to use fresh fuel with a stabilizer for longer shelf life. Happy mowing!

  19. Douglas Butler says:

    This article has made me reconsider how I store my lawnmower during the off-season. Great tips!

    • Allard Vdhooft says:

      Glad the article could help! Remember to store your lawnmower without the fuel during the off-season to prevent issues. Thanks for reading!

  20. Cameron Warren says:

    The video links included in the article were very helpful. Great additional resources!

    • Allard Vdhooft says:

      Thank you for your feedback, Cameron! I’m glad you found the video links helpful. Remember to use fresh fuel with a stabilizer to prevent gas from going bad. Happy mowing!

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