If your mower has been sitting unused for a while, especially over winter, removing the old fuel is the first and most important step to getting it running smoothly again.
Below is an easy, safe, and effective guide on how to get old gas out of a lawn mower, even if you’re a beginner.
How to Get Old Gas Out of Lawn Mower
What You Need Before Removing Old Gas
Before you begin, gather the following tools and safety items:
- Fuel siphon pump or turkey baster
- Clean gas container
- Funnel
- Adjustable pliers
- Shop towels or rags
- Safety gloves
- Safety glasses
- Fresh gasoline (preferably with fuel stabilizer)
Working with fuel can be hazardous, so make sure the area is well-ventilated and free of sparks or flames.
Step-by-Step:
1. Disconnect the Spark Plug for Safety
Safety comes first. Remove the spark plug wire from the plug to prevent accidental starting. This ensures the engine stays completely off while you work.
2. Access the Fuel Tank
Remove the fuel cap and position the mower on a flat, stable area. If the tank is easy to reach, you’ll be able to siphon directly from it. For riding mowers, fuel tanks are usually under the seat or hood.
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3. Use a Siphon Pump to Extract Old Gas
A siphon pump is the cleanest and safest tool for emptying the tank.
How to do it:
- Insert the siphon’s intake hose into the fuel tank.
- Place the outlet hose into your approved gas container.
- Pump until all old gasoline is removed.
If you don’t have a siphon pump, a turkey baster can work for push mowers, though it takes longer.
4. Remove the Fuel Line to Drain Remaining Gas
Most lawn mowers have a small rubber fuel line running from the tank to the carburetor. Use pliers to loosen the clamp, then disconnect the line.
Be prepared, gas may flow quickly. Direct it into your fuel container or place a small catch pan beneath the mower.
This step ensures all remaining old fuel leaves the system, not just the tank.
5. Check and Clean the Fuel Filter
Some mowers (especially riding mowers) have an inline fuel filter. If it’s clogged or dirty, replace it. A clogged filter restricts fuel flow and may prevent the mower from starting even with fresh gas.
6. Drain Old Gas from the Carburetor Bowl
The carburetor bowl holds a small amount of fuel, and if old fuel sits here, your mower may still stall or fail to start.
Here’s how:
- Locate the carburetor (usually near the air filter).
- Place a small cup or rag beneath the bowl.
- Loosen the bolt at the bottom of the bowl to release old fuel.
- Tighten the bolt once empty.
This step removes varnish-prone fuel that can cause clogs.
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7. Add Fresh Gasoline with Stabilizer
After you’ve removed all old fuel, refill the tank with fresh, high-quality gasoline. Adding a fuel stabilizer is highly recommended—this keeps your fuel fresh for up to 12 months and prevents future starting issues.
8. Reconnect the Spark Plug
Once everything is drained and refilled, reconnect the spark plug wire. Your mower is now ready to start with clean, effective fuel.
Why You Must Remove Old Gas
Gasoline contains volatile compounds that evaporate over time. Once degraded, it loses combustibility and forms residues. Old fuel can lead to:
- Difficulty starting the mower
- Rough idling or constant stalling
- Sticky buildup inside the carburetor
- Corroded fuel system components
- Reduced engine power
- Complete engine failure if ignored long-term
If your mower won’t start after storage, the fuel is often the main culprit.
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Tips to Keep Your Lawn Mower Running Smoothly
Use Fuel Stabilizer Every Season
Adding a stabilizer to every fresh fill can greatly extend the life of your mower’s fuel system.
Run the Mower Dry Before Storage
Before winter, let the mower run until it shuts off. This clears fuel from the carburetor and lines.
Use Fresh Gas Only
Avoid using gas older than 30 days unless a stabilizer was added on day one.
Store Gas Properly
Keep gasoline in an approved container away from heat sources and sunlight.
Inspect Your Carburetor Regularly
If the mower still struggles after draining the fuel, your carburetor might need cleaning or rebuilding.
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FAQs
How do you treat old gas in a lawn mower?
You can treat old gas in a lawn mower by removing it completely and replacing it with fresh fuel mixed with a fuel system cleaner or stabilizer. If the gas is only slightly old (less than 2–3 months) and hasn’t turned dark or gummy, you can sometimes dilute it by mixing one part old gas with three parts fresh gas plus a stabilizer.
However, if the gasoline is more than 3 months old or smells sour, it must be fully drained because no additive can restore severely degraded fuel.
How to drain gas from a riding lawn mower without a siphon?
To drain gas from a riding lawn mower without a siphon, you can disconnect the fuel line that runs from the tank to the carburetor. Place a clean fuel-safe container under the hose, loosen the clamp with pliers, and pull the hose off so the gas flows out.
Make sure the mower is off, the spark plug is disconnected, and the area is well-ventilated. This method completely empties the tank without the need for a siphon pump.
How long can gas sit in a lawn mower?
Gas can sit in a lawn mower for about 30 days before it begins to degrade. Without stabilizer, gasoline starts losing volatility within a month and can form varnish and gum in the carburetor. With a fuel stabilizer added on day one, gas can last up to 12 months, and in some cases up to 24 months depending on the brand and storage conditions.
What is the easiest way to drain a gas tank?
The easiest way to drain a gas tank is to use a hand siphon pump, which safely transfers fuel from the mower tank into a container with minimal mess. Simply insert the siphon hose into the tank, place the other end into a fuel container, and squeeze or pump until empty. If you don’t have a siphon, disconnecting the fuel line is the next easiest method.
How to remove stale gas from a lawn mower?
To remove stale gas from a lawn mower, siphon or drain the tank, disconnect the fuel line to release any remaining fuel, and empty the carburetor bowl by loosening its bottom bolt.
Once all stale gasoline is removed, refill the tank with fresh gas and optionally add a fuel system cleaner to help clear residue from the carburetor and fuel lines.
What is the best treatment for stale gasoline?
The best treatment for stale gasoline is complete removal followed by adding fresh gasoline with a high-quality fuel stabilizer or fuel system cleaner. Stabilizers can prevent fuel from going stale, but they cannot fully restore degraded gasoline. If the fuel is slightly old, a product like Sea Foam or STA-BIL can help clean the system after refilling with new fuel.
Final Thoughts
Removing old gas from a lawn mower is simple but critical maintenance that many homeowners overlook. By draining the tank, fuel line, and carburetor, and refilling with fresh gas, you can restore smooth performance, prevent future damage, and ensure your mower lasts for years. Following the steps above will help you get rid of stale fuel safely and get your mower running like new again.
