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Can You Use Old Gasoline in a Lawn Mower? The Definitive Guide

The short answer is: it’s generally not recommended to use old gasoline in your lawn mower. While a small amount of very slightly old gas might work, using stale gasoline can lead to a range of performance issues and potentially damage your mower’s engine.

Let’s delve into the reasons why and explore the best practices for fuel management in your lawn care equipment.

The Dangers of Old Gasoline

Gasoline, unlike fine wine, does not get better with age. It degrades over time, a process accelerated by exposure to air and moisture. This degradation leads to several problems that can negatively impact your lawn mower:

Varnish Formation: As gasoline ages, it forms varnish, a sticky residue that can clog fuel lines, carburetors, and fuel injectors. This can lead to starting problems, poor performance, and even engine failure.
Phase Separation: Ethanol-blended gasoline (which is most gasoline available today) is susceptible to phase separation. Ethanol absorbs water from the atmosphere. When the water content becomes too high, the ethanol and water separate from the gasoline, forming two distinct layers. The ethanol-water layer is corrosive and won’t burn properly, leading to significant engine problems.
Octane Degradation: Over time, gasoline loses octane, which can lead to engine knocking or pinging. This occurs when the fuel ignites prematurely in the cylinder, causing damage.
Reduced Combustion Efficiency: Stale gasoline doesn’t burn as efficiently as fresh gasoline, resulting in reduced power, increased fuel consumption, and higher emissions.

Using old gasoline in your lawn mower is like feeding it a slow poison. It may work temporarily, but the long-term consequences can be costly.

How to Tell if Gasoline is Old

Identifying old gasoline is crucial for preventing problems. Here are some telltale signs:

Time Since Purchase: As a general rule, gasoline starts to degrade after about 3-6 months, particularly if not stored properly. Gasoline that has been sitting for longer than six months should be treated with caution.
Color and Odor: Fresh gasoline typically has a clear, light amber color and a distinct smell. Old gasoline may be darker in color, have a sour or stale odor, or even smell like varnish.
Residue at the Bottom of the Container: If you see a layer of residue at the bottom of your gas can, it’s a clear sign that the gasoline has degraded.

Proper Gasoline Storage

Proper storage is essential for extending the life of your gasoline. Here are some tips:

Use a Sealed Container: Store gasoline in a tightly sealed, approved container to minimize exposure to air and moisture.
Add a Fuel Stabilizer: Fuel stabilizers prevent gasoline degradation and can extend its shelf life significantly (up to 24 months). Add a fuel stabilizer to the gasoline when you purchase it, especially if you don’t plan to use it immediately.
Store in a Cool, Dark Place: Store gasoline in a cool, dark, and dry location away from direct sunlight and heat. Temperature fluctuations can accelerate degradation.
Label the Container: Label the container with the date you purchased the gasoline. This will help you keep track of how old it is.
Avoid Metal Containers: While metal containers are durable, they can rust internally. If you do use a metal container, ensure it is specifically designed for gasoline storage and free of rust. Plastic containers designed for gasoline are generally a better choice.

What to Do with Old Gasoline

If you suspect your gasoline is old, here are a few options:

Dispose of it Properly: Do not pour old gasoline down the drain or onto the ground. Contact your local waste management facility for information on how to dispose of gasoline properly. Many communities have hazardous waste collection programs.
Mix it with Fresh Gasoline (with Caution): If the gasoline is only slightly old (a few weeks or months), you might be able to mix it with fresh gasoline in a 1:4 or 1:5 ratio. However, this is a risky approach, and it’s best to avoid it if possible. Always use a fuel stabilizer when doing this. If your lawn mower engine is particularly sensitive or valuable, it’s best to avoid this method altogether.
Use it as a Solvent: Old gasoline can be used as a solvent for cleaning greasy parts, but be sure to do this in a well-ventilated area and follow safety precautions.

Frequently Asked Questions (FAQs)

FAQ 1: How long can gasoline sit unused and still be good for a lawn mower?

Generally, gasoline can remain usable for about 3-6 months. Adding a fuel stabilizer can extend this period to up to 24 months. The actual lifespan depends on storage conditions and whether the gasoline contains ethanol.

FAQ 2: What is ethanol, and why is it a problem for lawn mowers?

Ethanol is an alcohol added to gasoline to increase octane and reduce emissions. While beneficial in some ways, it can cause problems in lawn mowers because it attracts water, leading to phase separation and corrosion of engine components.

FAQ 3: What is a fuel stabilizer, and how does it work?

A fuel stabilizer is a chemical additive that prevents gasoline from degrading. It works by inhibiting oxidation, preventing varnish formation, and stabilizing ethanol.

FAQ 4: Can I use gasoline with a higher octane rating than recommended for my lawn mower?

Using a higher octane rating won’t harm your engine, but it won’t provide any performance benefits either. Your lawn mower engine is designed to run on a specific octane level (usually 87).

FAQ 5: Is it okay to store my lawn mower with gasoline in the tank over the winter?

It’s generally not recommended to store your lawn mower with gasoline in the tank over the winter. Gasoline can degrade and cause problems. It’s better to drain the fuel or add a fuel stabilizer and run the engine for a few minutes to circulate the stabilized fuel through the system.

FAQ 6: What are the symptoms of using old gasoline in my lawn mower?

Symptoms include difficulty starting, poor performance, engine knocking or pinging, increased fuel consumption, and black smoke from the exhaust.

FAQ 7: Can using old gasoline damage my lawn mower engine?

Yes, using old gasoline can damage your lawn mower engine by causing varnish buildup, corrosion, and other problems that can lead to engine failure.

FAQ 8: What type of gasoline is best for my lawn mower?

Fresh, ethanol-free gasoline is the best option, especially for long-term storage. If ethanol-free gasoline isn’t available, use gasoline with a low ethanol content (E10 or less) and add a fuel stabilizer.

FAQ 9: How do I drain the gasoline from my lawn mower?

Refer to your lawn mower’s owner’s manual for specific instructions. Generally, you’ll need to disconnect the spark plug wire, locate the fuel line, and drain the gasoline into an approved container.

FAQ 10: What’s the difference between regular gasoline and premium gasoline?

The primary difference is the octane rating. Premium gasoline has a higher octane rating than regular gasoline. However, unless your lawn mower’s owner’s manual specifically recommends premium gasoline, there’s no benefit to using it.

FAQ 11: How often should I replace the fuel filter on my lawn mower?

It’s recommended to replace the fuel filter at least once a year, or more frequently if you’re using gasoline with ethanol or if you suspect the filter is clogged.

FAQ 12: My lawn mower won’t start after sitting for a while. What should I do?

First, check the spark plug and air filter. Then, consider if the gasoline is old. If it is, drain the fuel tank and carburetor, replace with fresh fuel, and try again. If the problem persists, you may need to clean the carburetor or consult a professional mechanic.

By understanding the risks associated with old gasoline and following these guidelines, you can keep your lawn mower running smoothly for years to come. Remember, a little preventative maintenance goes a long way in preserving the life of your equipment.