Many people – including myself – assume that it’s okay to use car gas in a lawn mower; gasoline is gasoline right?
The answer isn’t so simple. Even though lawn mowers will run on any type of gas, using the wrong one can damage your mower’s engine and void its warranty.
The best gas for lawn mowers is clean, fresh, and unleaded.
Ideally, you are looking for:
- Unleaded fuel with a minimum of 87 octane; a minimum of 85 octane if operating at high altitudes (over 5,000 feet)
- Gasoline with a maximum of 10% ethanol
Do not use E15 and E85 products. They are not designed for use in small engines and can cause engine damage and/or void the engine warranty
Do Lawn Mowers Take Regular Gas?
Ahh, the burning question: can you use regular car gas in lawn mower engines? In the short term, yes; using regular car gas in your mower is fine and will power your machine.
In the long term, however, using regular gas station fuel can be problematic as it contains ethanol. While ethanol is fine for cars, it can degrade your lawn mower over time.
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How does Ethanol Fuel Affect Lawn Mower Engines?
Ethanol fuel is a bio-fuel that is primarily obtained from sugarcane. It is hydrophilic – meaning it attracts water from the atmosphere. This water enters your fuel system and mixes with gas when the lawn mower engine is running.
This chemical mix of water and gas does two things:
- Dissolves deposits in the gas tank and fuel lines, and
- Corrodes the metal and rubber parts in the engine (including 20-in gas push mower models).
If you’re using your lawn mower often, like during the summer, the gas cycles through the system. In this case, using regular gas should be fine.
Problems arise when you leave regular fuel sitting in the gas tank of your mower long term — over winter, for example. Then, the leftover fuel can cause serious problems like those mentioned above. During the period of unuse, the gas can also become stale, leading to gummy deposits in the carburetor and rust accumulation.
What is an Octane Rating and Why Does it Matter?
If you are using regular gasoline, you will also want to consider the octane rating.
Octane ratings dictate the fuel’s ability to avoid “knock.” Knock occurs when fuel burns unevenly in your lawn mower’s engine cylinders. A higher rating means less chance of the gas exploding rather than burning.
There are three octane grades offered at most retail gas stations:
- 87 (regular)
- 89 (mid-grade)
- 91-93 (premium) at most retail gas stations
Most, but not all gasoline, contains up to 10 percent ethanol.
Ethanol has a higher octane number than gasoline and providers mix it with gasoline to enhance the octane rating.
What is the Best Gas for Lawn Mower?
I recommend using ethanol-free gas or unleaded gas in lawn mowers. Both will boost the longevity of your lawn mower, and other gasoline-powered outdoor power equipment.
Here are some of the common types of gas and whether you can use them in your mower or not.
Regular Unleaded Gasoline
You can use regular unleaded gasoline in lawn mowers.
Regular unleaded gasoline is a low-octane gasoline that contains 10 percent ethanol. It has a standard 87 octane. This is the lowest octane rating you can use in lawn mowers. (If you are in higher altitudes, then 85 octane is the lowest rating.)
As a bonus, unleaded fuel doesn’t contain any lead compounds. This makes it better for the environment and less hazardous to your health.
Mid-Grade Unleaded Gasoline
Mid-grade gasoline has an octane rating between 88 and 90. It is sold as premium gas at gas stations and costs more than regular unleaded gasoline.
Mid-grade fuel is not produced at gasoline refineries; instead, it is made at the pump. When you squeeze the mid-grade handle, regular and premium fuel are “splash blended” together to produce mid-grade unleaded gasoline.
At the end of the day, you can use mid-grade gasoline in your mower, but there are no added benefits.
Premium unleaded gasoline is generally between 92 and 93 octane fuel. It is the most expensive choice at gas stations.
You can use high-octane premium unleaded gas in your mower. Like with mid-grade gasoline, there are no extra benefits to premium gasoline.
E15 – E85 Gasoline
E15 and E85 are not recommended types of gas for lawn mowers.
Referred to as “flex fuels”, E15 and E85 are high-level ethanol-gasoline blends. They have somewhere between 15 percent ethanol to 83 percent ethanol.
As mentioned above, the smaller engines in lawnmowers aren’t designed to handle high-ethanol blends. Using them can corrode the lawn mower’s tank. It can also impact the lawn mower’s engine and other problems. This applies even to medium-sized riding mower models.
This isn’t just our opinion. For example, leading lawn mower manufacturer Briggs & Stratton warns customers:
Do not use unapproved gasoline, such as E15 and E85. Do not mix oil in gasoline or modify the engine to run on alternate fuels. Use of unapproved fuels will damage the engine components, which will not be covered under warranty.
See also my detailed article: ⛽ Accidentally Put Gas in the Oil Tank on your Lawn Mower?
Diesel should never be used in a lawn mower with a non-diesel engine. (Yes, believe it or not, non-diesel mowers do exist such as the Outlaw Renegade by Bad Boy Mowers.)
Diesel has a high-octane rating. So while it won’t harm your mower’s engine or engine equipment, it will cause to to run poorly.
Best Gas for Lawnmowers with 2-Stroke Engines
Any unleaded gas with an 87 to 93-octane rating will work well for 2-stroke engines.
That said, 2-stoke engines will need more oil lubrication than a 4-stoke engine.
This is because straight, unleaded gasoline doesn’t provide the necessary quality of lubrication. If used alone it will result in poor engine performance. (This goes without saying but, forcing an engine to run without proper lubrication will damage the piston and cylinders.)
The best oil-to-gas ratio depends on your manufacturer, make, and lawn mower model. The most common oil-to-gas ratio is 50:1.
Best Gas for Lawn Mowers with 4-Stroke Engines
Four stoke engines will be happy with any clean, fresh unleaded gas with 10 percent ethanol and minimum 87 octane.
Most four stoke mower engines accept gas directly so there’s no need to mix oil and gas. Instead, you can add the oil and gas in their dedicated slots.
If you aren’t sure whether you have a 2-cycle or 4-cycle engine, check the engine’s port:
- If it has a single opening, it’s a two-stroke engine, so you can add the oil and gas mix;
- If it has two tanks, it is a 4-stoke engine and you will add the oil and gas separately.
What is TruFuel and is it a Good Option for Gas-Powered Mowers?
TrueFuel is my go-to choice for my gas-powered mowers. It offers reliable engine performance for both my 2-cycle and 4-cycle engines.
TrueFuel is a high-octane, ethanol-free fuel formulated for 2-cycle mower engines. TrueFuel is available in common mixes such as 40:1 or 50:1. You can also order it in 4-stroke engine blends.
Best of all, this ethanol-free fuel is easy to use by simply opening the can, pouring it into gas tanks, and getting to work. No need to worry about the oil-to-gas ratio!
Unopened TrueFuel lasts for years. Once opened, it stays fresh for up to two years so there’s no loss to fuel wastage.
You can buy TrueFuel online or at your local hardware store.
- For best performance, follow the manufacturer's recommendations in your vehicle owner’s manual.
Affiliate links and images pulled from the Amazon Product Advertising API on: 2023-06-05
How Do I Keep Lawn Mower Gas Fresh for Long-Term Storage?
To keep your gas fresh while your lawn mower is in storage, you can do two things: (1) drain the gas, or (2) add a fuel stabilizer.
Generally, I do not recommend draining the gas from your fuel tank for storage. While some manufacturers do recommend this, there is a big risk of damaging your engine. Draining can also make it harder to start when you take it out of storage, can take a toll on peak performance, and also harms the carburetor.
Instead, if you’re going to store your mower for more than 30 days, add a high-quality fuel stabilizer to keep the fuel fresh for up to 24 months. This eliminates the need to drain your tank.
- STORAGE – STA-BIL Storage Fuel Stabilizer eliminates the need to drain fuel and keeps gasoline fresh for up to 24 months. Never fear your car or small engine refusing to start due to fouled fuel. This product is effective in all gasoline and ethanol blended fuels including E-10 through E-85
- ENSURES QUICK, EASY STARTS – Treating your gas with this fuel stabilizer prevents gum, varnish, rust, and corrosion in your fuel tank, all of which are costly to repair. The 32 oz. bottle of this alcohol-free fuel additive treats up to 80 gallons of fuel, and it is perfect to use prior to storing either your vehicle or outdoor power equipment for an extended period
- VERSATILE – STA-BIL Storage Fuel Stabilizer is safe for use in all gasoline engines, including 2-cycle. Use this fuel treatment in your vehicle, motorcycle, lawn mower, snow blower, boat, and generator
Affiliate links and images pulled from the Amazon Product Advertising API on: 2023-06-05
How do I Add a Fuel Stabilizer to My Lawn Mower?
First, ensure you have fresh gasoline in the tank and the tank is roughly 95 percent full. Next, pour the fuel stabilizer into the tank and run the mower engine for approximately 5 minutes. This will circulate the stabilizer through the fuel system.
Now you are ready to safely store your lawn mower and keep your fuel fresh for next season!
How to Know if Lawn Mower Gas is Bad?
There are some tell-tale signs that your lawnmower gas is bad:
- The mower has trouble starting or won’t start at all.
- If the engine starts but isn’t running smoothly, the bad gas is the likely culprit.
If you still aren’t sure if your lawnmower gas is bad, then you can perform a gas discoloration test by comparing the current gas in your mower with fresh gas. Gas will change color as it degrades, so this is a good way to determine if your gas is bad.
If you don’t want to take the trouble of removing a sample of gas from the tank, the last option is to sniff the gas in the tank. If it has a sour odor, it is bad. WARNING: do not smell gas as it’s extremely dangerous and hazardous to your health.
What if You Fill Up Your Mower with the Wrong Type of Fuel? How to Empty Bad Gas?
If you filled your tank with the wrong type of fuel, there’s no need to break a sweat yet! There are two approaches you can take to drain the gas from your mower. Needless to say, both require extreme care because you’re dealing with flammable gas.
You can use either a manual or mechanical siphoning pump to pull the fuel from the tank and into a canister. The other way is a bit tedious by using two hoses and gravity.
Here’s an informative video on choosing the right fuel for your mower:
Yes, you can use regular gasoline in your lawn mower, regardless of if you have a 2-stroke mower or 4-stroke mower. I recommend a minimum of 87 octane clean, fresh unleaded gasoline.
There is no need to upgrade to mid-grade or premium unleaded gasoline. Both types cost more but don’t offer any better performance. If you want the best-performing gasoline for your lawn mower, I recommend going with TrueFuel.
Hi, Alex Kuritz here. Growing up I remember that my family had one of the best lawns in the neighborhood. Richly green and lush. I did a lot as I grew up in terms of caring and tending for not only my family’s lawn but also my neighbors. I can say I have years of experience, and I am here to share it with you.