How Long Can You Leave Fuel in a Chainsaw?

Last Updated on June 29, 2025 by woodcutter

Chainsaws are indispensable tools for cutting firewood, pruning trees, or tackling storm cleanup, but improper fuel storage can lead to performance issues or costly repairs. Whether you’re a seasoned logger or a weekend DIYer, one question many chainsaw users face is: How long can you leave fuel in a chainsaw without causing damage? is simple: No longer than 30 days for ethanol gas, up to 90 days for ethanol-free, and up to 12 months for sealed commercial fuels.

Knowing how long you can safely leave fuel in a chainsaw—and how to store it properly—is key to maintaining its efficiency and longevity. This guide provides detailed insights into fuel storage limits, best practices, and tips to keep your chainsaw in top shape.

Why Fuel Storage Matters?

Chainsaws use a two-stroke fuel mixture of gasoline and oil, which lubricates the engine during operation. Unlike four-stroke engines with separate oil systems, two-stroke fuel degrades over time due to oxidation, evaporation, and (in ethanol-blended fuels) moisture absorption. Leaving fuel in the tank too long can cause gummed-up carburetors, clogged fuel lines, corrosion, and starting issues, all of which reduce performance and may require professional repairs.

How Long Can Fuel Stay in a Chainsaw?

The safe storage duration for fuel in a chainsaw depends on the fuel type, whether a stabilizer is used, and storage conditions:

• Mixed Fuel (No Stabilizer): A standard 50:1 or 40:1 gasoline and two-stroke oil mixture should be used within 30 days if left in the chainsaw’s tank. Beyond this, the fuel can separate, lose its combustibility, and form gummy residues that clog the carburetor and fuel system, leading to poor performance or engine damage (STIHL Fuel Mix Guide).
• Ethanol-Free Fuel with Stabilizer: Ethanol-free gasoline mixed with a fuel stabilizer (e.g., STA-BIL or STIHL Fuel Stabilizer) can remain in the tank for 3–6 months without significant degradation, provided the chainsaw is stored properly. Stabilizers prevent oxidation and gum formation, but for storage beyond 6 months, draining the tank is recommended (Madsen’s Shop).
• Ethanol-Blended Fuel (E10): Gasoline with up to 10% ethanol (E10) is safe for regular use but absorbs moisture from the air, leading to phase separation and corrosion within 2–4 weeks if left in the tank. This can damage fuel lines, seals, and carburetors, so E10 should be drained sooner than ethanol-free fuel.
• For casual users or seasonal workers, pre-mixed, ethanol-free fuel (such as STIHL MotoMix or TruFuel) is a smart choice. These fuels come stabilized and can last up to 2 years unopened and about 12 months after opening, making them

Follow The 30-Day Rule: When to Use or Lose the Fuel?

As a general rule of thumb, you should not leave fuel in your chainsaw for more than 30 days—especially if you’re using standard pump gasoline. After about a month, fuel begins to oxidize and break down, especially if it contains ethanol, a common additive in most fuels. Ethanol attracts moisture from the air, which can lead to corrosion in the carburetor, fuel separation, and starting difficulties.

Even with a tightly sealed fuel tank, ethanol-blended gas can absorb moisture and degrade. This degradation forms gummy deposits in your fuel system, leading to rough idling, loss of power, or even complete failure to start.

Factors That Affect Fuel Storage

Several factors influence how long fuel can safely remain in a chainsaw:

• Fuel Type: Ethanol-free gasoline is more stable than E10 because it doesn’t attract moisture, which causes phase separation and corrosion. High-ethanol blends like E15 or E85 are unsuitable for chainsaws and degrade rapidly, causing damage.
• Storage Conditions: Store the chainsaw in a cool, dry, well-ventilated area away from direct sunlight and heat sources. High temperatures accelerate fuel breakdown, while humidity increases moisture absorption in ethanol-blended fuels.
• Two-Stroke Oil Quality: High-quality synthetic oils, such as STIHL Ultra or Husqvarna Premium, include additives that enhance fuel stability compared to lower-quality oils. These oils reduce the risk of separation and residue formation (FarmstandApp).
• Fuel Stabilizers: Adding a stabilizer to fresh fuel significantly extends its shelf life by slowing oxidation and preventing gum buildup. Follow the product’s instructions (typically 1 oz per 2.5 gallons of fuel) for optimal results.

Best Practices for Fuel Storage

To ensure your chainsaw remains in good condition, follow these storage guidelines:

1. Mix Only What You Need: Prepare enough fuel for 30 days of use to avoid storing old fuel. For a 50:1 ratio, mix 100ml of two-stroke oil with 5 liters of gasoline in a clean, approved fuel canister (STIHL Canisters).
2. Use Ethanol-Free Fuel: Opt for ethanol-free gasoline, especially for chainsaws used infrequently or stored for extended periods, as it resists moisture absorption and degradation.
3. Add a Fuel Stabilizer: For storage beyond 30 days, add a fuel stabilizer to fresh fuel. Products like STA-BIL can keep fuel stable for up to 12 months in a sealed container, though 3–6 months is safer in the chainsaw’s tank.
4. Store Properly: Keep the chainsaw in a cool, dry, well-ventilated area. Avoid extreme heat, freezing temperatures, or humid environments, which can degrade fuel and damage the tank.
5. Drain for Long-Term Storage: For storage exceeding 3–6 months, drain the fuel tank completely and run the chainsaw at idle until the carburetor is dry. This removes residual fuel, preventing clogs and corrosion.

Signs of Bad Fuel

If fuel has been left in the chainsaw too long, you may encounter these issues:

• Difficulty Starting: Degraded fuel loses its volatility, making it harder to ignite in the engine.
• Rough Idling or Stalling: Gummy residues from old fuel can clog the carburetor, disrupting fuel flow and causing inconsistent performance.
• Excessive Smoke: Separated oil in the mixture can lead to poor combustion, producing excessive smoke.
• Corrosion or Residue: Ethanol-blended fuels may leave sticky deposits or corrode metal components, particularly in the fuel system.

To address bad fuel, drain the tank, clean the fuel system with carburetor cleaner, and refill with fresh, properly mixed fuel. If problems persist, consult a professional technician, such as a STIHL dealer (STIHL Dealers).

Premixed Fuels: A Convenient Option

Premixed fuels, such as STIHL MotoMix or Husqvarna XP+ Fuel, are ethanol-free and pre-stabilized, offering a shelf life of up to 2 years in a sealed container or 6–12 months in the chainsaw’s tank. These fuels eliminate mixing errors and provide consistent performance, making them ideal for infrequent users or those prioritizing convenience. However, they come at a higher cost, so consider your usage frequency and budget (FarmstandApp).

Safety and Maintenance Tips

• Mix and Refuel Safely: Always mix fuel in a well-ventilated area, away from open flames or sparks. Refuel with the engine off and at least 3 meters from the work area. Clean up spills immediately and change clothes if fuel contacts them to prevent fire risks.
• Dispose of Old Fuel Properly: Take degraded or old fuel to a local recycling center or hazardous waste facility. Never pour it down drains or onto the ground, as this is environmentally harmful.
• Follow Manufacturer Guidelines: Check your chainsaw’s owner’s manual for specific fuel and storage recommendations to ensure compliance with warranty requirements.
• Regular Maintenance: Periodically inspect the fuel system, including the tank, lines, and carburetor, for signs of residue or corrosion. Clean or replace components as needed to maintain performance.

Chainsaw Fuel Myths—Busted

Myth #1: “I can just top off the old gas with new gas.”
Reality: Mixing old and fresh fuel doesn’t refresh the old—it just contaminates the new. Always drain the tank fully before refilling.

Myth #2: “Premium gasoline from the pump is ethanol-free.”
Reality: Most premium fuels still contain up to 10% ethanol. To be safe, look for gas labeled specifically as ethanol-free or buy commercial pre-mixed fuel.

Myth #3: “Stabilizers make gas last forever.”
Reality: Fuel stabilizers slow oxidation but don’t stop it. Even stabilized gas has a shelf life and should be used within 2–3 months if possible.

Conclusion: Keep It Fresh, Keep It Running

Fuel can safely remain in a chainsaw for up to 30 days without a stabilizer, or 3–6 months with ethanol-free fuel and a stabilizer, provided the chainsaw is stored in a cool, dry environment. For storage beyond this period, drain the tank and run the carburetor dry to prevent clogs, corrosion, and performance issues. Using ethanol-free gasoline, high-quality two-stroke oil, and a fuel stabilizer, along with proper storage practices, will keep your chainsaw reliable and ready for action. Always consult your owner’s manual for model-specific guidance to ensure optimal performance and avoid warranty issues.

Frequently Asked Questions

Should I empty my chainsaw after use?

Yes, it’s a good idea to empty your chainsaw’s fuel tank after use—especially if you don’t plan to use it again soon. Fuel left in the tank can degrade over time, especially if it contains ethanol, leading to starting issues, gummed-up carburetors, and fuel system damage. To prevent this, drain the fuel and run the engine until it stops to clear any remaining fuel from the system. However, if you use your chainsaw frequently, within a few days or weeks, storing it with fresh, stabilized fuel may be more convenient.

How long can fuel sit out for?

Fuel can start to go bad in as little as 30 days, especially if it contains ethanol. Ethanol-blended fuel attracts moisture from the air, which can lead to separation, corrosion, and poor engine performance. After about a month, the fuel’s quality begins to degrade, making it harder for your chainsaw to start or run properly. To extend its shelf life, you can add a fuel stabilizer, which helps keep the fuel usable for up to 12 months. For best performance and to avoid engine issues, always use fresh, properly mixed fuel in your chainsaw.

How long can you leave 2-stroke fuel?

You can typically leave 2-stroke fuel for up to 30 days without problems, especially if it contains ethanol. After that, it begins to degrade, which can cause hard starting, poor performance, or engine damage. If you add a fuel stabilizer, the mix can last up to 3 to 12 months, depending on storage conditions and the stabilizer used. For best results, always store 2-stroke fuel in an airtight, approved fuel container, away from heat and sunlight, and mix only what you expect to use within a few weeks.

Is it okay to leave bar oil in a chainsaw?

Yes, it’s generally okay to leave bar oil in a chainsaw between uses, especially if you plan to use it again soon. Bar and chain oil doesn’t degrade as quickly as fuel and won’t harm the saw when left in the oil reservoir. However, if you’re storing the chainsaw for a long time (e.g., several months), it’s a good idea to drain the bar oil to prevent leaks, as some chainsaws may slowly leak oil when not in use. Storing the saw on a protective surface or emptying the oil tank can help keep your workspace clean and prevent mess.

Is it bad to leave fuel in a chainsaw?

Yes, it can be bad to leave fuel in a chainsaw, especially for extended periods. Fuel—particularly if it contains ethanol—can degrade in as little as 30 days, leading to gum and varnish buildup in the carburetor and fuel lines. This can cause hard starting, poor performance, or even engine damage. If you plan to store the chainsaw for more than a few weeks, it’s best to drain the fuel tank and run the engine until it stops to clear any remaining fuel. Alternatively, use a fuel stabilizer to extend the fuel’s life for up to 12 months.

How long can gas sit in a chainsaw?

Gas can safely sit in a chainsaw for about 30 days before it starts to degrade, especially if it contains ethanol. After that, the fuel can break down, absorb moisture, and form varnish or gum deposits that clog the carburetor and fuel system. This can make the chainsaw hard to start or run poorly. If you need to store it longer, add a fuel stabilizer to extend the life of the gas up to 3–12 months, or drain the tank and run the saw dry for long-term storage.

Should you store a chainsaw with fuel in it?

It’s generally not recommended to store a chainsaw with fuel in it for long periods. Fuel—especially if it contains ethanol—can degrade within 30 days, causing gumming, clogging, and starting issues. If you plan to store the chainsaw for more than a few weeks, it’s best to drain the fuel tank and run the engine until it stops to clear any remaining fuel from the system. For short-term storage (under a month), you can leave fresh fuel in the tank, ideally with a fuel stabilizer added to prevent degradation. Proper storage helps extend the life of your chainsaw and keeps it ready to use.

How to store a chainsaw without oil leaking?

To store a chainsaw without oil leaking, follow these steps:

1. Empty the bar oil reservoir – Drain the oil tank if you won’t be using the chainsaw for an extended period. This prevents leaks caused by pressure buildup or gravity.
2. Clean the saw – Wipe off any excess oil and sawdust, especially around the bar, chain, and oil ports.
3. Store it upright – Always store the chainsaw in an upright position (flat on its base). Avoid storing it on its side, as this can encourage oil to seep out.
4. Use an oil drip tray or pad – Place the chainsaw on a protective surface like a tray or absorbent pad in case of minor leaks.
5. Check the oil cap – Make sure the oil cap is tight and in good condition. A damaged or loose cap can lead to leaking.

By following these tips, you can reduce or prevent oil leaks during storage.