How Long Can Gas Sit In A Lawn Mower Safely?

Can you use old gas in a lawn mower? Yes, but only for a limited time, and it’s generally not recommended to let gasoline sit in your lawn mower for extended periods.

Letting gasoline sit in your lawn mower is a common concern for many homeowners. We all want our equipment to work when we need it, and understanding how long fuel remains viable is key to preventing frustrating lawn mower starting issues. This guide will delve into the specifics of gasoline shelf life and how it impacts your beloved mower.

How Long Can Gas Sit In A Lawn Mower
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The Lifespan of Gasoline

Gasoline is a complex mixture of hydrocarbons. When exposed to air, heat, and light, it begins a process called gas degradation. This process isn’t sudden; it’s a gradual breakdown of the fuel’s components.

Factors Affecting Gas Degradation

Several factors contribute to how quickly gasoline goes bad:

Air Exposure: Oxygen in the air reacts with gasoline, leading to oxidation. This creates gummy deposits and varnishes that can clog fuel lines and carburetors.
Heat: Higher temperatures accelerate the degradation process. Storing gasoline in a hot garage or shed will cause it to break down faster than in a cool, stable environment.
Light: UV rays can also contribute to fuel breakdown, although this is less of a concern when the fuel is stored in a sealed container.
Ethanol Content: Modern gasoline often contains ethanol, an alcohol additive. Ethanol fuel problems are a significant factor in fuel degradation.

Ethanol’s Role in Fuel Degradation

Ethanol is added to gasoline for several reasons, including boosting octane and reducing emissions. However, ethanol is hygroscopic, meaning it attracts and absorbs water from the air. This water can then separate from the gasoline, creating a phase separation.

Phase Separation: When water and ethanol separate from the gasoline, they tend to sink to the bottom of the tank. This can lead to a corrosive mix that damages metal components in your fuel system.
Gum and Varnish Formation: Ethanol can also react with certain metals and rubber components, leading to the formation of sticky gums and varnishes that impede fuel flow.

How Long Does Gasoline Last?

The general consensus is that fresh gasoline will last about 30 to 90 days if left untreated in a sealed container. However, when it’s in your lawn mower’s fuel tank, it’s exposed to more variables.

Gasoline in a Lawn Mower

Once you put gasoline in your lawn mower, its usable life often decreases. Factors like the mower’s fuel tank material (plastic versus metal), the presence of the fuel cap’s venting system, and ambient temperature all play a role.

Plastic Tanks: Plastic tanks can allow more air exchange than metal tanks, potentially speeding up degradation.
Metal Tanks: While more resistant to air exchange, metal tanks can be susceptible to rust if water is present, especially when using ethanol-blended fuels.

For practical purposes, lawn mower fuel storage in the tank itself is best kept to a few weeks if you want to avoid issues.

Signs of Old or Degraded Gas

Recognizing the signs of bad gas is crucial to preventing damage to your lawn mower.

What to Look For:

Cloudy Appearance: Fresh gasoline is clear and has a slight yellowish tint. Degraded gas may appear cloudy or have sediment at the bottom.
Foul Odor: Old gasoline can develop a stale, varnish-like smell instead of the usual sharp gasoline odor.
Separation: If you can see distinct layers in the fuel, especially a layer of water or a milky substance, the fuel has likely undergone phase separation.

Potential Problems with Old Gas in Mower

Using old gas in mower engines can lead to a cascade of problems, ranging from minor performance issues to costly repairs.

Common Issues:

Starting Difficulties: The most common symptom is the mower becoming difficult to start or refusing to start altogether. This is due to clogged fuel lines, carburetors, or a lack of proper combustion from degraded fuel.
Rough Running: Even if the mower starts, it might run roughly, sputter, stall, or have reduced power. This indicates inconsistent fuel delivery or poor fuel quality.
Clogged Fuel Filter: The fuel filter can become clogged with gum and varnish, restricting fuel flow.
Carburetor Damage: The gummy residue from old gas can clog the tiny jets and passages in the carburetor, requiring a thorough cleaning or even replacement.
Fuel Pump Failure: In mowers with electric fuel pumps, degraded fuel can cause these pumps to fail.
Internal Engine Damage: In severe cases, corrosive byproducts from degraded fuel can damage internal engine components.

Best Practices for Lawn Mower Fuel Storage

Proper lawn mower fuel storage is essential to maximize the life of your gasoline and protect your equipment.

Storing Gasoline Safely

Use Approved Containers: Always store gasoline in a clean, approved portable fuel container. These are typically made of plastic or metal and have tight-fitting lids.
Cool, Dry Place: Store containers in a cool, dry, well-ventilated area away from direct sunlight, heat sources, and open flames. Garages or sheds are common places, but avoid storing it near water heaters or furnaces.
Seal Tightly: Ensure the container lid is tightly sealed to minimize air exposure and prevent vapors from escaping.
Label Clearly: Label the container with the date you purchased the gasoline. This helps you track its age.
Avoid Contamination: Never store gasoline in containers that previously held other liquids, like water or chemicals, as contamination can quickly ruin the fuel.

The Role of Fuel Stabilizers

This is where fuel stabilizer benefits truly shine. A quality fuel stabilizer is designed to prevent the degradation of gasoline, especially when it’s going to be stored for an extended period.

How Stabilizers Work:

Antioxidants: Stabilizers contain antioxidants that slow down the oxidation process.
Detergents: Some stabilizers include detergents that help keep fuel system components clean and prevent gum formation.
Corrosion Inhibitors: These help protect metal parts from corrosion, especially when ethanol-treated fuels are used.
Water Dispersants: Certain stabilizers can help keep small amounts of water dispersed in the fuel, preventing phase separation.

When to Use a Fuel Stabilizer:

Seasonal Storage: The most common time to use a fuel stabilizer is when storing lawn mower and other outdoor power equipment for the off-season (fall and winter).
Infrequent Use: If you only use your mower a few times a year, adding stabilizer to each tank can be beneficial.
Before Long Storage Periods: Even for a few months, adding stabilizer to the tank before storing the mower can prevent future problems.

How to Use Fuel Stabilizers:

Add to Fresh Fuel: Always add the stabilizer to fresh gasoline before putting it into the mower’s tank or your storage container. This ensures the stabilizer mixes thoroughly with the fuel.
Follow Instructions: Adhere strictly to the dosage instructions on the stabilizer’s product label. Overdosing is generally not harmful, but it’s wasteful.
Run the Engine: After adding the stabilizer and filling the tank, run the engine for 5-10 minutes. This allows the treated fuel to circulate through the entire fuel system, including the carburetor. This is a critical step for effective fuel system maintenance.

Draining Lawn Mower Fuel: When and How

Sometimes, the best course of action is to remove the old fuel entirely. This is especially true if the gas has been sitting for many months or shows signs of degradation.

When to Drain:

Gas Older Than 6 Months: If you didn’t use a stabilizer and the gas is over 6 months old, it’s best to drain it.
Signs of Degradation: If the fuel looks cloudy, has a foul odor, or shows signs of separation, drain it immediately.
Before Long-Term Storage: Even if the gas isn’t “old,” it’s good practice to either drain the tank or fill it with stabilized fuel before long-term storage.

How to Drain Lawn Mower Fuel:

There are a few methods for draining lawn mower fuel:

Siphon Method:
- You’ll need a siphon pump (hand pump or electric) and an approved container for the old fuel.
- Insert one end of the siphon hose into the mower’s fuel tank and the other into the collection container.
- Start the siphon action (by pumping the handle or priming the electric pump).
- Be careful not to spill any fuel.
Drain Plug Method:
- Some mowers have a drain plug at the bottom of the fuel tank or carburetor bowl. Consult your owner’s manual to see if your mower has one and where it’s located.
- Place an approved container underneath the drain plug.
- Use an appropriate wrench to loosen and remove the drain plug.
- Allow the fuel to drain completely.
- Once drained, clean the plug and re-install it, ensuring it’s snug but not overtightened.
Carburetor Bowl Drain:
- Many carburetors have a small screw or bolt at the bottom of the bowl. Loosening this will drain the fuel from the carburetor itself.
- This is a good step if you’re only draining the fuel from the carburetor for maintenance.

Important Note: Dispose of old gasoline responsibly. Do not pour it down drains or onto the ground. Contact your local waste disposal facility for proper disposal guidelines.

Fuel System Maintenance Tips

Regular fuel system maintenance is crucial for the longevity and performance of your lawn mower.

Proactive Steps:

Check Fuel Lines: Periodically inspect fuel lines for cracks, leaks, or stiffness. Replace them if they show signs of wear.
Clean Carburetor: If you experience running issues, cleaning the carburetor can often resolve the problem. This might involve removing the carburetor bowl to clean out any sediment.
Replace Fuel Filter: Many mowers have a fuel filter. Replace it according to the manufacturer’s recommendations, usually annually.
Use Fresh Fuel: Whenever possible, use fresh gasoline. If you buy gas in bulk for storage, consider adding a stabilizer to it immediately.

Storing Lawn Mower for the Winter

Proper storing lawn mower for the winter is critical to prevent issues when spring rolls around.

Winterizing Steps:

Fuel Treatment: This is the most important step for the fuel system.
- Option A (Recommended): Fill the fuel tank with fresh gasoline and add the correct amount of fuel stabilizer. Run the engine for 5-10 minutes to ensure the stabilized fuel circulates through the carburetor and fuel lines.
- Option B (Draining): Drain all fuel from the tank and carburetor. You can use the siphon method for the tank and then run the engine until it sputters and dies, which will help clear the carburetor bowl. This method is effective but can leave some seals and gaskets prone to drying out if the mower is stored for very long periods.
Oil Change: Change the engine oil. A fresh oil change ensures better lubrication and prevents acidic contaminants from sitting in the crankcase.
Clean the Mower: Clean the mower deck, engine housing, and any other parts. Remove grass clippings and debris to prevent rust and corrosion.
Spark Plug: Consider removing the spark plug, squirting a small amount of engine oil into the cylinder, and then slowly turning the engine over manually a few times. This lubricates the cylinder walls. You can then reinstall the spark plug.
Battery: If your mower has an electric start, remove the battery and store it in a cool, dry place. Connect it to a trickle charger or maintainer if possible.
Storage Location: Store the mower in a clean, dry, and protected area, such as a shed or garage. Covering the mower can help protect it from dust and debris.

Frequently Asked Questions (FAQ)

Q1: Can I mix old gas with new gas in my lawn mower?

While technically possible, it’s generally not advisable if the old gas is significantly degraded. Mixing a small amount of old gas with fresh, stabilized gas might work, but if the old gas is rancid or has visible contaminants, it can spoil the fresh gas and still cause problems. It’s better to use fresh, stabilized fuel or drain the old gas entirely.

Q2: What happens if I run old gas in my mower?

Running old gas can lead to the mower not starting, running poorly (sputtering, low power), or even causing damage to the carburetor, fuel lines, and other fuel system components due to gum, varnish, and potential corrosion.

Q3: How much stabilizer should I add?

Always follow the instructions on the fuel stabilizer product label. They are usually measured per gallon of gasoline. For example, a product might say “1 ounce treats 5 gallons.”

Q4: How long does stabilized gas last?

Stabilized gasoline can last for a much longer period, often 6 to 24 months, depending on the quality of the stabilizer and storage conditions. However, for optimal performance of your lawn mower, it’s still best to use fuel that is within a year of treatment if possible.

Q5: Is it okay to leave gas in my mower over the summer if I use it regularly?

If you use your mower frequently throughout the summer, and the gas is only a few weeks old, it’s generally fine. The key is to avoid letting untreated gasoline sit stagnant for long periods. If you notice the gas is getting older than a month without use, consider adding a stabilizer or using it up and refilling with fresh fuel.

By following these guidelines, you can ensure your lawn mower is ready to go when you are, minimizing the risk of lawn mower starting issues and costly repairs. Proper lawn mower fuel storage and consistent fuel system maintenance are your best allies.