How Long Can Gas Sit In A Lawn Mower Safely? A Fuel Guide

Can you leave gas in a lawn mower over winter? Yes, you can, but it’s not ideal and can lead to problems. Leaving gasoline in your lawn mower for extended periods, especially over several months, can result in stale gas, which can cause significant issues for your equipment. This guide will help you understand the fuel life of your lawn mower fuel and how to protect your fuel system from potential engine damage.

How Long Can Gas Sit In A Lawn Mower
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The Lifespan of Gasoline: What Happens Over Time

Gasoline, particularly modern ethanol-blended fuel, is not a stable substance. Over time, it undergoes a process called gasoline degradation. This degradation affects the fuel’s performance and can leave behind harmful deposits.

Factors Influencing Gasoline Degradation:

Ethanol Content: Most gasoline sold today contains ethanol, an alcohol added to improve octane ratings and reduce emissions. Ethanol is hygroscopic, meaning it attracts and absorbs water from the air. This absorbed water can lead to phase separation, where the ethanol and water mixture settles at the bottom of the fuel tank, leaving the remaining gasoline with a lower octane and increased corrosiveness.
Oxidation: Exposure to oxygen in the air causes gasoline to oxidize. This process creates gummy residues and varnish-like deposits. These sticky substances can clog fuel lines, carburetors, and fuel injectors.
Evaporation: Lighter, more volatile components of gasoline evaporate over time, especially in warmer temperatures. This leaves behind a heavier, less potent fuel that can be harder for the engine to ignite and burn efficiently.
Temperature Fluctuations: Storing gasoline in areas with significant temperature swings can accelerate the degradation process. Condensation can form inside the tank, contributing to water absorption.

How Long is “Too Long”? A Timeline for Lawn Mower Fuel

So, how long can gas sit in a lawn mower safely? Generally, fresh gasoline can begin to degrade noticeably within 30 days when left untreated in a fuel tank. However, this is a broad estimate, and several factors influence this timeframe.

Short-Term Storage (1-2 Months):

For periods of one to two months, particularly during the mowing season, leaving gasoline in your lawn mower is usually acceptable, provided it’s relatively fresh. However, even within this timeframe, some minor degradation might begin.

Medium-Term Storage (2-6 Months):

As you approach the two-month mark, the risk of stale gas increases. If you anticipate not using your mower for this period, especially during the summer months when heat can accelerate degradation, it’s wise to take precautions.

Long-Term Storage (6 Months and Beyond):

This is where leaving gas in your lawn mower becomes a significant risk. For long-term storage, such as over the winter, leaving untreated gasoline in the tank is strongly discouraged. The potential for phase separation, gumming, and corrosion is much higher, leading to potential engine damage.

The Perils of Stale Gas: Risks to Your Lawn Mower

Using stale gas in your lawn mower can lead to a cascade of problems, affecting various parts of the fuel system and the engine itself.

Common Issues Caused by Stale Gas:

Carburetor Problems: The gummy residues and varnish from degraded fuel are notorious for clogging the tiny jets and passages within the carburetor. This can result in an engine that is difficult to start, runs rough, stalls, or won’t run at all.
Fuel Line Blockages: Similar to carburetors, fuel lines can become blocked by the deposits left behind by stale gas. This restricts the flow of fuel to the engine, causing it to sputter and die.
Fuel Filter Clogging: If your lawn mower has a fuel filter, it can become clogged with the sediment and debris from degraded fuel, reducing fuel flow.
Corrosion: Water absorbed by ethanol-blended fuel can lead to rust and corrosion within the fuel tank and other metal components of the fuel system.
Reduced Engine Performance: Even if the fuel hasn’t completely gummed up the system, the chemical changes in the gasoline can lead to reduced power, poor acceleration, and increased fuel consumption.
Engine Damage: In severe cases, the lack of proper fuel flow and the presence of contaminants can lead to overheating and significant engine damage, potentially requiring costly repairs or even replacement.

Best Practices for Lawn Mower Fuel: Ensuring Longevity

To avoid the pitfalls of stale gas and protect your lawn mower’s fuel system, adopting good fuel management practices is crucial. These practices are especially important when considering seasonal storage or long-term storage.

Using a Gas Stabilizer: Your Fuel’s Best Friend

One of the most effective ways to combat gasoline degradation is by using a gas stabilizer. A gas stabilizer is a fuel additive designed to prevent the fuel from breaking down.

How Gas Stabilizers Work:

Antioxidants: They contain antioxidants that slow down the oxidation process, preventing the formation of gums and varnishes.
Detergents: Some stabilizers include detergents that help keep fuel system components clean and prevent deposits from forming.
Corrosion Inhibitors: These additives protect metal parts from rust and corrosion, especially important with ethanol-blended fuels.

When to Use a Gas Stabilizer:

Before Storage: The best time to use a gas stabilizer is before you store your lawn mower for any significant period, especially for seasonal storage or long-term storage.
Regularly: Even if you use your mower frequently, adding a stabilizer to your gasoline can help maintain fuel quality, particularly if you buy gas in larger quantities and store it in a separate container.

How to Use a Gas Stabilizer:

Add to Fresh Fuel: Always add the stabilizer to fresh gasoline before putting it into the lawn mower’s tank.
Run the Engine: After adding the stabilizer to the fuel in your mower’s tank, start the engine and let it run for a few minutes. This ensures the treated fuel circulates throughout the entire fuel system, including the carburetor and fuel lines, coating all internal components.
Follow Product Instructions: Always follow the specific dosage instructions on the gas stabilizer product you purchase. Different brands and formulations may have slightly different recommendations.

Choosing the Right Gasoline:

Freshness: Always buy gasoline from a reputable station with high turnover. This ensures you’re getting the freshest fuel possible.
Ethanol Content: If available, consider using ethanol-free gasoline for your lawn mower, especially for long-term storage. Ethanol-free fuel is more stable and less prone to water absorption and phase separation. However, it can be more expensive and harder to find.
Storage of Gasoline: If you store gasoline in portable containers, use approved fuel containers and store them in a cool, dry, well-ventilated area away from direct sunlight and ignition sources.

Proper Fuel Management Techniques:

Empty the Tank: For extended periods of long-term storage, the safest approach is to drain the fuel tank completely. Run the engine until it stops from lack of fuel, which helps clear the carburetor as well.
Use a Fuel Additive: If you cannot drain the tank, always use a gas stabilizer. This is the most practical solution for most users.
Cleanliness: Keep your lawn mower clean, especially around the fuel cap and filler neck. Dirt and debris can enter the fuel tank and contaminate the fuel.

Preparing Your Lawn Mower for Seasonal Storage

Proper preparation for seasonal storage is key to preventing engine damage and ensuring your lawn mower starts up reliably next season.

Step-by-Step Guide to Seasonal Storage Preparation:

Run the Mower Dry (Optional but Recommended): As mentioned, running the mower until it runs out of fuel is an excellent way to clear the carburetor and fuel lines. This prevents stale gas from hardening inside these crucial components.
Add a Fuel Stabilizer (If Not Running Dry): If you choose not to run the mower dry, fill the fuel tank with fresh gasoline and add the recommended amount of gas stabilizer. Then, run the engine for 5-10 minutes to allow the stabilized fuel to circulate throughout the entire fuel system.
Change the Oil: Fresh oil protects the engine from corrosion and wear during storage. It’s generally a good practice to change the oil before long-term storage, as used oil can contain corrosive acids.
Clean the Mower: Thoroughly clean the entire mower, including the deck, engine housing, and wheels. Remove grass clippings and debris, which can hold moisture and cause rust or corrosion.
Inspect and Service: Check the air filter, spark plug, and blades. Clean or replace them as needed. Sharpening the blades will ensure better performance next season.
Store Properly: Store your lawn mower in a dry, protected location, such as a garage or shed. Avoid damp or humid environments. Cover the mower with a breathable tarp to protect it from dust and moisture.

Can I Use Old Gas from a Car in My Lawn Mower?

While it might seem like a good idea to use up old gasoline from your car, it’s generally not recommended for your lawn mower. Car gasoline is often a mix of various grades and additives, and if it’s been sitting in your car for a long time, it’s also susceptible to gasoline degradation. The risk of introducing stale gas and causing engine damage to your lawn mower is high. It’s always best to use fresh, appropriate lawn mower fuel or fuel specifically treated for small engines.

The Impact of Ethanol on Lawn Mower Fuel Systems

Ethanol’s presence in gasoline has a significant impact on small engines like those found in lawn mowers.

Ethanol’s Double-Edged Sword:

Pros: Ethanol can help boost octane and reduce certain emissions.
Cons:
- Water Absorption: As noted, ethanol attracts water, leading to phase separation.
- Corrosiveness: Ethanol can corrode certain rubber and plastic components found in older fuel systems. Many modern small engine manufacturers design their fuel systems to be compatible with ethanol, but older equipment may be at risk.
- Gumming: Ethanol can contribute to the formation of gums and varnishes more quickly than non-ethanol fuels.

Recommendations for Ethanol Blends:

Check Your Owner’s Manual: Always consult your lawn mower’s owner’s manual for specific recommendations regarding fuel types and ethanol content.
Use Stabilized Fuel: If you must use ethanol-blended fuel, ensure it is fresh and consider using a gas stabilizer to mitigate the negative effects.

When to Seek Professional Help

If you’ve experienced issues with stale gas or suspect your fuel system has been compromised, it’s best to consult a qualified small engine mechanic. They can diagnose the problem and perform the necessary repairs, saving you from further engine damage.

Frequently Asked Questions (FAQ)

Q1: How long can gasoline safely sit in a lawn mower without a stabilizer?

Gasoline can begin to degrade within 30 days without a stabilizer, especially in warmer temperatures or if it contains ethanol. For extended periods beyond a month or two, it’s risky.

Q2: What are the signs of stale gas in a lawn mower?

Signs include difficulty starting, rough idling, stalling, loss of power, and a “gummy” or varnish-like residue in the fuel tank or carburetor.

Q3: Can I just add stabilizer to old gas?

While adding a gas stabilizer can help slow down further degradation, it won’t reverse the damage already done by stale gas. It’s best to add stabilizer to fresh fuel. If you suspect the gas is already significantly degraded, it might be better to drain and dispose of it properly.

Q4: How often should I use a gas stabilizer?

For long-term storage or seasonal storage, use a stabilizer every time you fill the tank. If you use your mower frequently, you can add it every few months as a preventative measure.

Q5: Does storing gasoline in a metal container make it last longer?

Yes, storing gasoline in approved metal containers can help maintain its quality better than some plastic containers, as they offer better protection against air and light, which contribute to degradation. However, a gas stabilizer is still the most effective way to extend fuel life.

Q6: What is phase separation?

Phase separation occurs in ethanol-blended fuels when the ethanol attracts enough water that it separates from the gasoline and settles at the bottom of the tank. This water-ethanol mixture is corrosive and can cause engine damage.

Q7: Is it okay to use premium gas in my lawn mower?

Most lawn mowers are designed to run on regular unleaded gasoline. Using premium gas generally offers no benefit and can be more expensive. Always check your owner’s manual for the recommended octane rating.

Q8: What are fuel additives?

Fuel additives are substances added to gasoline to improve its performance or stability. Gas stabilizers are a type of fuel additive.

By following these guidelines, you can ensure your lawn mower’s fuel system remains in good condition, preventing engine damage from stale gas and ensuring it starts reliably whenever you need it. Proper fuel management is a small investment of time that pays off in the longevity and performance of your equipment.