If you have an engine, whether it’s on your car or lawn mower, you’ve probably wondered: does gasoline go bad? Unfortunately, bad gas can be a headache. Knowing the symptoms and how long it takes for gas to go bad is key to staying ahead of potential problems. I’ve dealt with a few engines and have devised a few methods to ensure gas lasts as long as possible and keeps the engine running smoothly. I’ll share them below.
Does Gasoline Go Bad? (The Short Answer)
If left unprotected, the shelf life of gasoline is minimal at 30 days. Gasoline will degrade naturally through a chemical process, leaving fuel unusable. Avoidable environmental factors can further accelerate this chemical process.
What Happens to Gas Over Time?
Whether your fuel is stored in an engine’s fuel tank or a gas can, you’ve likely asked yourself: does gas expire, or how long does gas last? Unfortunately, all gas has an expiration date. Microbes such as aerobic and anaerobic bacteria begin to form in gasoline. The more that these microbes grow, the less combustible the fuel is. Adding to these problems is the reduction of volatility and oxidization through the environment over time.
Factors that Can Impact How Long Gas Lasts
It really comes down to environmental factors when questioning how long gasoline lasts or when it goes bad. Gas degrades no matter what, but the wrong conditions can shorten how long gas is good for. The main ones are:
Direct Sunlight & Warming Gasoline
Once gasoline starts warming up from direct sunlight or warm environments, it evaporates and vaporizes. The first parts of gasoline to evaporate are the parts engines need to ignite. If gasoline is left to evaporate long enough, it will lose all combustibility and be rendered completely useless for engines.
Contact With Oxygen & Metal
If gasoline comes into contact will oxygen and metal, it will oxidize. This can be observed when gasoline changes to an amber/brown color. Additionally, oxidizing gasoline containing ethanol will draw water vapor/condensation into the fuel. The result is gum residue, and water in the fuel.
Signs that Indicate Your Gas Has Expired
Once the gas begins to expire, your engine will have several noticeable problems. The following are typical symptoms of bad gas in a lawn mower.
- Difficulty starting up the engine
- Unstable idling
- Stalling
With the fuel worsening over time, you’ll notice these symptoms become more apparent. You’ll spend more time trying to start the mower, and the engine will stall regularly.
Best Practices to Ensure Your Gas Lasts As Long As Possible
The most common question I get is: how long does it take for gas to go bad? Generally speaking, whether in your mower or a can, gasoline typically starts to degrade after 30 days. However, it can degrade even faster if kept under the wrong conditions. I’ll share several “Best Practices” you can use to increase your fuel’s life span and ensure it lasts the full 30 days. Let’s take a look at what these are.
Storing Your Lawn Mower Somewhere Suitable
Having a cool, shaded storage location for your lawn mower is definitely a good practice to maintain. Keeping the mower out of direct sunlight and heat will reduce evaporation.
Use Plastic Gas Cans
Using a plastic gas can rather than a metal can will limit oxidization.
Using a Tight Seal
Ensure a tight seal on the storage gas container and the lawn mower’s gas tank. Reducing the fuel’s contact with air will increase the life span of the fuel by reducing evaporation and oxidation.
Store Small Amounts of Gasoline
When storing gasoline, ensure that you only have gas that will be used within 30 days. Excess gasoline that cannot be used within this period will expire, and that’s just wasteful.
How to Stop Fuel Going Bad After 30 Days
When someone asks me if gasoline goes bad and is there a way to stop it? I share a simple solution to this inevitable problem: fuel stabilizers.
There are a number of different products available on the market, and you can achieve months of storage with them. If you are using your fuel within 30 days, you may not need a stabilizer.
However, if you want to leave your lawn mower unused for extended periods or store gas in a container for more than 30 days, then a fuel stabilizer is the best solution. Stabilizers stop/reduce chemical processes within gasoline caused by sunlight, heat, contact with air, and metals. This means you can extend the fuel’s lifespan to over twelve months quite easily.
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