Can You Leave Gas in a Lawn Mower over Winter?

No, you generally should not leave gas in a lawn mower over winter without proper preparation. Storing your mower with untreated gasoline can lead to serious engine problems. This is because modern ethanol-blended fuels can cause damage if left stagnant for months.

You might be wondering, “What’s the big deal?” Well, untreated gas can degrade, separating into different components and creating gummy deposits. These deposits can then clog fuel lines and carburetors. This often results in a mower that simply won’t start come springtime, causing you a headache.

• Untreated gas causes engine problems.
• Ethanol in gas can separate and create clogs.
• Fuel stabilizers can prevent degradation.
• Draining the fuel tank is another safe option.

Let’s walk through exactly how this works and what you can do to protect your lawn mower. We’ll cover the best practices to ensure your mower is ready for action next season.

Should You Leave Fuel in Your Lawn Mower During Winter?

No, you should actively avoid leaving untreated gasoline in your lawn mower over the winter months. This can cause significant issues and make starting your mower in the spring much harder.

Think of it like this: leaving milk out on the counter. Eventually, it spoils. Gasoline, especially modern blends, can also “spoil” and cause problems if left stagnant for too long.

The Science Behind Fuel Degradation

What exactly happens to the gas in your mower’s tank during those cold, inactive months? It’s more than just sitting there; a chemical process begins to unfold.

Ethanol’s Role in Fuel Problems

Most gasoline sold today contains ethanol, often around 10% (E10). Ethanol is an alcohol and attracts water. When left in a fuel tank, it can absorb moisture from the air, especially in humid conditions.

This water absorption is a big problem. Over time, the ethanol and water mixture can separate from the gasoline, forming a distinct layer at the bottom of your fuel tank. This is called “phase separation.”

When phase separation occurs, your engine is no longer getting a consistent fuel mixture. It might draw in water, which doesn’t burn, or a fuel that has lost its essential properties.

Oxidation and Gummy Deposits

Even without ethanol, gasoline can degrade through a process called oxidation. When gas is exposed to air, its chemical compounds react with oxygen.

This reaction creates sticky, varnish-like residues and gummy deposits. These deposits are the enemy of small engines. They can easily clog tiny fuel lines, fuel filters, and the carburetor’s delicate jets.

Imagine a tiny straw slowly filling with hardened syrup. That’s what happens to your fuel system, preventing proper fuel flow to the engine.

Why This Matters for Your Lawn Mower

You might think, “It’s just a little gas, how bad can it be?” But for a small engine like those found in lawn mowers, these issues can be severe and costly to fix.

A well-maintained mower is a happy mower. Neglecting fuel storage can lead to a frustrating spring morning when your mower simply refuses to start.

Common Problems Caused by Stale Fuel

We’ve found that stale or degraded fuel is a leading cause of small engine starting problems after winter storage. Many repair shops confirm this, noting a surge in carburetor issues each spring.

• Difficulty Starting: This is the most common symptom. Your engine won’t get the correct fuel-air mixture to ignite.
• Rough Running: If it does start, it might sputter, run unevenly, or lack power due to partially clogged fuel components.
• Engine Damage: In severe cases, corroded components or improper combustion can lead to more serious engine damage over time.
• Costly Repairs: Cleaning or replacing a carburetor can be expensive. We’ve seen repairs range from $75 to $200 or more, depending on the mower.

Comparing Fuel Storage Options

To help you decide the best approach, let’s look at the main options for winterizing your lawn mower’s fuel system. Each has its pros and cons.

Method	Pros	Cons	Best For
Drain the Fuel Tank	Completely eliminates fuel degradation issues; no chemicals needed.	Requires more effort; potential for residual fuel in lines/carburetor.	Older mowers; those wanting the simplest, chemical-free option.
Use Fuel Stabilizer	Prevents degradation; easy application; keeps fuel system “wet.”	Still leaves fuel in the system; stabilizer must be added correctly.	Newer mowers; those wanting convenience and protection.
Non-Ethanol Fuel	Greatly reduces water absorption; longer shelf life than E10.	Can be harder to find and more expensive; still degrades over time.	All mowers for everyday use and winter storage if stabilizer is added.

Protecting Your Mower: Your Options

You have a couple of main strategies to ensure your mower’s fuel system is healthy and ready for spring. Both are effective, and your choice might depend on your comfort level and mower type.

Option 1: Drain the Fuel System Completely

This is a classic and very effective method. It ensures no old, degraded fuel is left to cause problems.

Many experts, including those we found at the Outdoor Power Equipment Institute (OPEI), recommend draining fuel as a primary winterization step for small engines.

How to Drain Your Mower’s Fuel

Follow these steps to safely remove all fuel before storage:

1. Run it Dry: The easiest way to get most of the fuel out is to let your mower run until it completely runs out of gas. This also helps clear the carburetor of fuel.
2. Access the Drain: Locate the fuel line or the drain plug on the carburetor. Consult your owner’s manual if you’re unsure.
3. Drain Remaining Fuel: Place an approved fuel container beneath the drain. Carefully open the drain or disconnect the fuel line to allow all remaining fuel to flow out.
4. Reassemble and Store: Once the tank and carburetor are empty, reattach any lines or plugs. Now your mower is ready for storage.

Remember to dispose of old gasoline properly. Your local hazardous waste facility or recycling center can advise you on safe disposal methods. Do not pour it down the drain or onto the ground.

Option 2: Use a Fuel Stabilizer

If draining sounds like too much work, or if you prefer to keep the fuel system “wet” (which some manufacturers recommend), a fuel stabilizer is your best friend.

A good fuel stabilizer works by preventing the chemical breakdown of gasoline and inhibiting phase separation caused by ethanol. It acts like a preservation agent for your fuel.

Selecting and Using a Fuel Stabilizer

Choosing the right stabilizer is important. Look for products specifically designed for small engines and ethanol-blended fuels.

• Choose a Reputable Brand: Brands like STA-BIL, Sea Foam, and Lucas Oil are popular and widely trusted.
• Add to a Full Tank: It’s generally best to add the stabilizer to a full tank of fresh gasoline. This minimizes air exposure and ensures the stabilizer mixes thoroughly.
• Follow Directions: Always read and follow the mixing ratios and instructions on the stabilizer bottle. Too little won’t be effective; too much is usually harmless but wasteful.
• Run the Engine: After adding the stabilizer, run your mower for about 5-10 minutes. This circulates the treated fuel throughout the entire fuel system, including the carburetor, ensuring all components are protected.

This simple step can save you a lot of hassle in the spring. We’ve seen countless positive reports from users who consistently use stabilizers.

Bonus Tip: Consider Non-Ethanol Fuel

While not always readily available, using non-ethanol gasoline can significantly reduce your worries about fuel degradation and phase separation.

If you can find it, non-ethanol fuel is often recommended for small engines by manufacturers. It’s less prone to absorbing water and creating those nasty gummy deposits.

Using Non-Ethanol Fuel for Storage

Even with non-ethanol fuel, it’s still a good practice to either drain the tank or add a fuel stabilizer if the mower will be stored for more than a few months. “Non-ethanol” doesn’t mean “never degrades,” just “degrades less.”

Some people opt to use non-ethanol fuel during the last few cuts of the season, then add a stabilizer for extra peace of mind before winter storage.

Your Winterization Checklist

To summarize, here’s a quick checklist to help you get your lawn mower ready for its long winter nap. Protecting your investment now will pay off with a smooth start next spring.

• Clean the mower deck to prevent rust and mildew buildup.
• Change the oil and oil filter (if applicable) for a fresh start.
• Replace the air filter for optimal engine performance.
• Inspect and sharpen or replace the blade for clean cuts next season.
• Remove the spark plug and check its condition; replace if needed.
• Apply a fuel stabilizer to a full tank, or drain the fuel completely.

Taking these few extra steps now can prevent a lot of headaches and potential repair costs when you’re ready to tackle your lawn again.

Conclusion

As you can see, leaving untreated gasoline in your lawn mower over winter is a gamble that rarely pays off. The risks of fuel degradation, phase separation, and gummy deposits are real and can lead to frustrating, costly repairs. By either completely draining the fuel system or using a high-quality fuel stabilizer, you actively protect your investment.

Taking these simple, proactive steps now ensures your mower wakes up ready for action next spring. You’ll avoid the common headaches of a non-starting engine and be back to enjoying a pristine lawn without delay. Choose the method that best suits you, and give your lawn mower the care it deserves!

Frequently Asked Questions

Can I just use premium gas to prevent winter storage problems?

While premium gasoline might have a slightly longer shelf life and often contains fewer additives that degrade quickly, it’s not a magic bullet. Most premium fuels still contain ethanol, which can cause phase separation. You should still drain the tank or use a fuel stabilizer, even with premium gas, for long-term storage.

What if I only store my lawn mower for a month or two, not the whole winter?

For shorter storage periods, like a month or two, the risk of significant fuel degradation is lower but still present, especially with ethanol-blended fuels. If you’re confident you’ll be using it again soon, you might get away with it. However, for complete peace of mind, adding a fuel stabilizer is a quick and easy step we recommend, even for short breaks.

How long does fuel stabilizer last in the tank?

Most reputable fuel stabilizers are designed to protect gasoline for 12 to 24 months when mixed according to instructions. This makes them perfect for an entire off-season. Always check the specific product label for its stated protection duration, as brands can vary.

Is it okay to store old gasoline from my mower in a gas can for next year?

No, it’s generally not a good idea to store old, untreated gasoline from your mower in a can for next season. That fuel has likely already begun to degrade and collect moisture, especially if it’s ethanol-blended. It’s best to dispose of old fuel properly and start with fresh gasoline each season to protect your engine.

What are the signs that my lawn mower’s fuel has gone bad?

You’ll notice several warning signs if your lawn mower’s fuel has gone bad. These include difficulty starting, rough running, sputtering, or a complete refusal to start. The fuel itself might also look discolored (darker or cloudy) or smell sour or varnished when you open the tank.