Can I Use Motor Oil in a Lawn Mower?

You can use some types of motor oils in some kinds of lawn mower engines. However, as you may have already guessed, the answer isn't quite that simple. In most situations and for most lawn mowers, SAE 30 oil is the go-to lubricant. Here are the reasons and the factors to consider before using a different type of oil in yours.

Gas-powered lawn mowers operate using either two-stroke or four-stroke internal combustion engines. Four-stroke mower engines have replaced two-stroke models over the years. However, some two-stoke models are still around.

You can quickly identify which one you have by simply looking at the mower. Four-stroke engines have an oil reservoir separate from the gas tank, while two-stroke models don't since you'll need to mix the oil into the fuel before putting it in the machine.

Typically, residential riding and walk-behind lawn mowers run on small, air-cooled engines that can reach temperatures of 300 degrees Fahrenheit. Regular automotive motor oils, such as 5W-30 or 10W-40, are best for use in larger, liquid-cooled engines that top out at around 200 degrees.

Therefore, to maximize the life of your mower, oil designated for use in small engines is best for protecting small motors that run at higher temperatures.

Motor oils come in various weights. The weight measures how viscous or thick the oil is, or more accurately, how thick the oil acts at specific temperatures. If an oil has two numbers, the first of which is followed by a W, which stands for winter, then it's a multigrade oil that works well across a wide range of temperatures. The first number measures viscosity when the oil is cold, and the second measures the same at full operating temperature.

A multigrade oil isn't ordinarily necessary in lawn mowers because they're not often in operation when it's cold outside. However, the lower viscosity at cool temperatures won't generally harm a small engine.

Modern, high-quality oils aren't just oil. They come with additives and detergents that offer extra engine protection and add various qualities. Small engine oils have a few additives, such as zinc, that protect against wear at higher operating temperatures. In contrast, standard motor oils contain several additives and rely less on zinc and more on detergents optimized for larger engines.

Oils designed for lawn mowers and other small engines are different from the standard motor oil that you'd put in your automobile. However, on a basic level, they're very similar.

The best oil for your lawn mower is always the one that the manufacturer recommends in the user manual. The second choice is high-quality, small-engine SAE 30 motor oil if you're unsure of the manufacturer's suggestion.

Finally, if you occasionally run your lawn mower at temperatures below 40 degrees Fahrenheit or are in a bind when changing your mower's oil, a high-quality conventional or synthetic 5W-30 is likely OK for use in your lawn mower.