Are Lawn Mowers 4 Cycles?

I’ve stated it before, but I really enjoy mowing the yard. I hadn’t given it much thought when moving my sturdy mower up and down the grass to make those nice stripes, but what is most lawn mower motors these days — 2 or 4 stroke? What’s the difference, exactly?

Most lawn mowers are now 4 cycles since 2 cycle mowers have been phased out across the United States. The fuel and oil must be combined in a two-stroke (or two-cycle) engine. The oil and gasoline for a four-stroke (or four-cycle) engine are kept separate in two tanks.

Let’s take a closer look at everything and talk about the differences between the two engines – and what it means for their use…

What’s the Difference Between a 2 and 4 Stroke Lawn Mower?

The fuel and oil must be combined in a two-stroke (or two-cycle) engine. The oil and gasoline for a four-stroke (or four-cycle) engine are kept separate in two tanks.

2 stroke engines have fewer working components and need fewer stages. They are less difficult to maintain. A two-stroke engine is often smaller, lighter, noisier, smokier, and less expensive.

A four-stroke engine uses less gasoline and provides more torque. 4 stroke engines are also more dependable, powerful, and costly than 2 stroke engines.

Internal combustion engines are included in both engines. On the intake stroke of a four-stroke internal combustion engine, fuel and air are combined inside a chamber. The compression stroke places the mixture under pressure. The combination is then ignited by a spark plug, resulting in an explosion.

A combustion (or power) stroke occurs when an explosion forces a piston to move. The pistons are connected to the rotating crankshaft. The exhaust stroke is when the exhaust is finally discharged.

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The difference between a 2-stroke and a 4-stroke engine is the speed with which the combustion cycle takes place and the number of times the piston goes up and down during each cycle.

Each revolution of a four-stroke engine sees the piston perform one compressive and one exhaust stroke. The spark plugs only ignite once per four strokes or every other rotation.

The combustion cycle of a two-stroke engine is completed in one piston stroke. Every rotation, the spark plugs ignite once.

Here’s a quick reference guide to the differences (with videos of engines).

What Is the Difference Between a 2 and a 4 Stroke Mower? (Is it possible to tell just by looking at it?)


First, consult your handbook. Check to see if there are any additional indicators, such as stickers that read “No Fuel Mixing” to indicate a four-stroke mower.

Check the fuel cap next. If your mower has a two-stroke engine and the original gasoline cap is still attached, the cap will read the mix ratio (like 32:1). On a two-stroke engine, you won’t find a dipstick or separate fuel and oil ports. There is just one.

If your mower is four-stroke, you should have little trouble finding a dipstick. 4 stroke engines will have separate oil and fuel fill openings that will be clearly identified.

Why are two-stroke engines prohibited in the United States?

The term “banned” is a strong one. “Phased out” is a better word. New two-stroke engines will be phased out starting in July 2019 (unless they are fuel-injected). You can, however, continue to use your old 2-stroke outboard motors or dirt motorcycles, since they are not “prohibited.”

The truth is that two-stroke engines do not fulfill contemporary pollution rules, therefore you won’t find any new ones unless they are fuel-injected. In the United States, Europe, Australia, and a few other nations, new two-stroke engines are prohibited from being imported and sold.

The difficulty is that two-stroke engines don’t burn the oil/gas combination efficiently, so a lot of it ends up in the air or water. Since the 1940s, this wasteful engine design has remained unaltered.

According to the EPA, up to 30% of the oil/gas mixture you put into your engine is released unburned into the air or rivers, wasting 30% of your money.

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Old 2-stroke engines, according to the EPA, have leaked more oil into our rivers than the Exxon Valdez did in 1989. Yikes!

Importing and selling two-stroke engines is prohibited in the United States. You may still utilize an old 2-stroke engine (outboard motor, dirt bike) if you have one.

However, when it dies and you need to replace it, there are no new 2-stroke engines available. Privately owned 2-stroke engines are frequently accessible. Look into Craigslist.

Many countries still produce and sell two-stroke engines. In South America, Africa, and Asia, new two-stroke engines may be purchased.

Some 2-stroke engine manufacturers, such as Evinrude, Suzuki, Honda, and Yamaha, claim to have improved their 2-stroke engine emissions. Direct fuel injection is used in these two-stroke engines.

What Happens When You Pour 2 Stroke Oil in a 4 Stroke Mower?

It’s fine if you put two-stroke oil in a four-stroke engine once.

A solvent is added to 2 stroke engine oils to assist them to combine with gasoline. As a result, 2-stroke oil is a little thinner. It will also be free of the additives that are commonly present in 4-stroke oil.

It may smoke a bit more (one person described it as “like a freight train”), and your four-stroke engine may run a little hotter, according to experts. Others speculate that you may have extended the life of the 4-stroke engine by a year.

Examine your owner’s handbook for any warranty-voiding small print.

What kind of fuel does a four-stroke mower use? (Instead of a two-cycle?)

First and foremost, consult your owner’s handbook. Gas for four-stroke engines should have an octane rating of 87 or higher, while chainsaws require an octane rating of 89 or higher.

Ethanol levels in gasoline should range from 0% to 10%, with up to 15% MTBE (methyl tertiary butyl ether).

Ethanol with tiny four-stroke engines does not mix well. E85 gas, which contains 15% ethanol, should be avoided. Because ethanol produces water in a tiny engine, it may be difficult to start. Furthermore, ethanol is caustic and produces a lot of heat when burned, which might cause your engine to overheat.

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Gasoline and oil must be combined for 2 stroke engines. Check your instructions, but most two-stroke engines have a gas-to-oil ratio of 40:1, 32:1, or 50:1.

Make sure your gasoline is fresh because it can degrade in as little as 30 days. Consider adding a fuel stabilizer to the can if you know you’ll be storing gasoline for an extended period of time.

Will a four-stroke lawn mower engine be ruined by mixed fuel?

If you unintentionally pour a 2-stroke oil/gas mixture into the gas tank of a 4-stroke engine and notice it soon away, empty the gas tank — no damage, no foul. A minimal amount of oil will be consumed by the fire.

If you pour a 2 stroke oil/gas mixture into a 4 stroke engine’s fuel tank and start it, you’ll get a lot of smoke. Your engine may run rough, and your spark plugs may become fouled. The jets may become clogged if the engine is fuel-injected. If the gasoline line becomes clogged with oil, it may need to be replaced.

Drain the oil tank after pouring 2-stroke oil/gas into a 4-stroke engine’s oil tank. You can remove the oil tank if tipping the lawn mower doesn’t completely drain it. You may need to use some mild dishwashing soap to clean out the oil tank. Rinse it carefully after washing it. Allow the inside air to dry or use compressed air to do so.

Examine your warranty. Using mixed fuel in a four-stroke engine can sometimes violate the warranty.

Final Words

Two-stroke engines have been phased out across the US, therefore if you walk into a store to buy a new lawn mower, the engine will be four-stroke.

This does not exclude you from using your old two-stroke, as they have not been outlawed entirely.

What this means is that the most recent response to the question “are lawn mowers two or four cycles?” is that the majority are now four strokes. I hope this information is useful.

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