What Fuel Should I Use in My Lawn Mower?

Whether you’ve just bought a brand new lawn mower, or you’re wheeling out your old trusty machine, you’ll need some fuel to get the engine fired up. Though you might not think so, small engines can be particular about the kind of fuel they use. When faced with a bunch of different pumps at the gas station it can be kind of tricky to determine which one to choose. With varying fuel types, labeling, and a range of prices, it can be hard to find clear information about the fuel that you’re buying. Let’s talk about the different types of fuel and identify what kind of gas works best for lawn mowers.

What Fuel Should I Use in My Lawn Mower? (The Short Answer)

In general, lawn mower engines require unleaded gasoline with an octane rating of at least 87 and an ethanol content of 10% or less (most regular, mid-range, and premium unleaded gasoline fuels meet these requirements). This is true for both 2 stroke and 4 stroke engines. But, while 4 stroke engines burn only gasoline, 2 stroke engines run on a mixture of unleaded gasoline and two cycle engine oil. To give you a visual, here’s a table with common types of fuel and whether or not they can be used in a lawn mower:

Do Lawn Mowers Take Regular Gas or Something Else?

If you want to know what fuel lawn mowers use, there are a handful to pick from. Most of the time, yes, mowers take regular gas. However, not all regular gas has the exact same octane. Typically regular gas is 87 octane which works fine for all lawn mowers. In any case, I’ll describe the characteristics of each fuel type that you can use in a lawn mower engine below.

Regular Unleaded Gasoline

The most widely used fuel is regular unleaded gas. Again, it is usually rated at 87 octane, and available at every gas station. This is usually the lowest octane gasoline that you can buy, and usually the cheapest option. Also, this happens to be the lowest octane gasoline that you should use in a lawn mower or any small engine. Octane is a measurement of how much compression gasoline can handle before it combusts. Lower octane fuels can handle less compression, and higher octane fuels can handle more compression. This measurement is important because fuel and air are compressed over and over again in order to power gasoline engines.

Mid-Range Unleaded Gasoline

Gasoline with octane ratings between 88 and 90 are typically sold as mid-range or “plus” fuels. With a slightly higher octane, this type of gas can handle a bit more compression and is a little bit more expensive. If your gas station offers a regular gas that has an octane rating less than 87, you’re better off going with a mid-range or premium fuel option.

Premium Unleaded Gasoline

High octane or premium grade unleaded gasoline is usually rated at 91. Some gas companies might offer 92 or 93 octane fuel as their most expensive choice, but that’s a little bit less common. Certain car manufacturers recommend the use of premium unleaded gas due to its high octane rating, but whether or not it’s worth the extra money for lawn mowers is hotly debated by some people. To be honest, in my opinion premium gas for lawn mowers is not usually a necessary expense. Still, you can definitely use high octane unleaded gas in small engines if you’d prefer.

Non-Oxygenated Gasoline

To talk about non-oxygenated gasoline, let’s talk about oxygenated gas first. Most gasoline is oxygenated. This means that there are fuel additives called oxygenates added to boost fuel combustion and octane ratings. This, in turn, reduces exhaust emissions. The most common fuel additive containing oxygenates is ethanol. Because of this, nearly all oxygenated gasoline contains some ethanol. Non-oxygenated gasoline, on the other hand, is gasoline that does not have any ethanol in it.

But why would people want to use fuel without oxygenates/ethanol? Well, increasing the amount of oxygen in gasoline can lead to contamination from moisture. To make a long story short, some people like to use non-oxygenated gasoline in engines that aren’t operated on an every-day basis so that there is less risk of moisture messing up the fuel system. This type of gasoline tends to be on the more expensive end and is usually not widely available.

The Gas I’d Recommend You Use

Still asking yourself, what fuel should I use in my lawn mower? My recommendation is to either use regular unleaded, or non-oxygenated gasoline. These two fuels are pretty different so you might be wondering why I suggest using either one. Well, let me explain when it’s ideal to use each one.

Regular Unleaded Gasoline

When it comes to my push mower, I always go for regular unleaded gasoline. Though it has a lower octane, I have found that it performs the same as mid-range and premium fuels. I like saving a couple bucks, and I simply don’t think the higher compression rating of more expensive fuels is necessary when it comes to lawn mower engines.

Non-Oxygenated Gasoline

Being able to find non-oxygenated gasoline is the first step. Though it can be tricky to find in some areas, non-oxygenated gasoline is a great fuel option for all types of mowers. In my case, I only use non-oxygenated gasoline in my riding lawn mower. You really don’t want moisture to make its way into your fuel system, especially when you’re dealing with a machine that is so expensive. Non-oxygenated gas doesn’t have any ethanol in it and can help prolong the life of your lawn mower’s engine.

Fuels You Don’t Want to Use in Your Lawn Mower + Why

Though you can use a lot of different kinds of fuel in lawn mowers, there are some that do not agree with lawn mower engines. Below are two fuels that you should avoid.

High Ethanol Content Gasoline Blends

A lot of people aren’t aware of this, but almost all gasoline in the United States (and most other countries) contains up to 10% ethanol. This is the case for regular, mid-range, and premium unleaded gasoline. Any fuel containing more than 10% ethanol is categorized differently such as E15 with 15% ethanol or E85 with 85% ethanol. While these fuels have their uses, it is not a good idea to put them in your lawn mower. Small engines and high ethanol fuels don’t play nicely together because fuels with a high ethanol content can cause corrosion.

Diesel

This might go without saying, but diesel fuel should never be put into a gasoline engine (The same is true for diesel engines and gasoline). You are going to find yourself in a world of hurt if you put diesel in your lawn mower, and your small engine mechanic might never forgive you. Always make sure to double check what fuel you’re pumping when you’re at the gas station.

2 Stroke or 4 Stroke Mower: How This Affects Your Fuel Choice

There is really just one big difference when it comes to 2 stroke and 4 stroke engine fuel: 2 stroke engines burn a fuel and oil mix while 4 stroke engines burn only gas and keep engine oil in a separate reservoir. If you have a two stroke lawn mower you will need to mix in a set ratio of high quality 2 stroke engine oil each time you fill the gas tank. Using the right gas to oil ratio in a 2 stroke engine is extremely important. Aside from this distinction, 2 stroke and 4 stroke mowers require the same type of gas.