Cars and lawnmowers require oil to lubricate their engines, so killing two birds with one stone may seem smart. But is it possible to use one oil for both?

You can use car oil in a lawnmower as long as the viscosity grade matches. Most lawnmowers use SAE-30, and multigrade car engine oil often has the same upper viscosity, making it safe. However, you should check your lawnmower’s manufacturer specifications to be sure of that number.

I’ll dive into the specifics of engine oil and what it all means throughout the rest of this article.

What Type of Oil Should I Put in My Lawnmower?

You can put synthetic or conventional oil in your lawnmower, but you should choose the grade according to your mower’s specifications. If your mower has a 4-stroke motor, the same oil you typically use in your car should be fine.

In most cases, car oil will allow the lawnmower engine to perform even better as the multigrade viscosity will allow optimal performance at different temperatures.

Despite the convenience of only carrying and using one bottle of oil for both your car and lawnmower, one downside is that it can be pretty expensive. Higher performance oil like synthetic or synthetic blend is meant for higher performance engines, so using it on your mower may be overkill, but it may also last longer.

What’s the Difference Between Car Oil and Lawnmower Oil?

Cars and lawnmowers both have engines requiring lubricating, but not all oil is created equal.

Car engine oil is ‘multigrade,’ which means that the viscosity – or thickness – remains near-optimal at different temperatures. Most households use lawnmowers in warmer temperatures, so the oil only needs one grade.

Using cars across multiple seasons requires oil that performs under different conditions, making them require a different type of oil.

While different oil grades are more common in certain climates, car oil is normally fine in a lawnmower engine. However, there are exceptions to that rule.

Car Engines Compared to Lawnmowers

Car engines operate using a system of multiple pistons moving up and down to keep things moving. That said, they’re a lot more complicated than lawnmower engines. However, the combustion engine basics between car and lawnmower engines are similar.

What’s different is the fact that lawnmower engines come in two types.

Two-Stroke Motors

This is a complicated topic, but the essentials are that ‘two’ in ‘two-stroke’ has to do with the movement of the pistons.

Each full upward and downward movement counts as one stroke, meaning that pistons in two-stroke motors move up and down once each during the engine’s revolution.

Two-stroke engines have different parts and require a different type of lubricant made of a mixture of gas and oil. Using regular car engine oil on a two-stroke engine would lead to it not working properly and breaking down, so check what type of motor your lawnmower uses before adding car oil.

Four-Stroke Motors

Pistons in these engines move up and down twice each in one revolution, for four total strokes. These days all cars have four-stroke engines, and many lawnmowers do too. You would lubricate these engines with pure oil that isn’t mixed with anything else.

Car Oil Grade

This is arguably the most important thing to consider when buying car engine oil at the shop because it tells you how the oil will perform at different temperatures.

As car oil is multigrade, it will have two numbers, and one of the most common multigrades you’ll find is 10W-30. The ‘W’ stands for ‘winter,’ and the 10 next to it tells you how thick the oil is in those cold conditions. The lower that first number is, the thinner it is.

The number to the right tells you how viscous the oil is in warmer conditions. In other words, multigrade oil works to keep your car engine running smoothly regardless of whether it’s hot or cold.

Different Viscosities of Oil

As you know by now, different viscosity oil is recommended for different engines and climates. But what exactly is the difference, and what happens when you use one that’s slightly different from what’s recommended?

Low Viscosity Oil

A bottle of oil with smaller numbers written on it means that the oil is generally thinner. Thin oil is important for lower temperatures and is specified for some engines, but it isn’t all-purpose.

At higher temperatures, the oil will be too thin, leading to more friction in the engine. This can result in severe wear and tear on the motor parts as well as burning oil.

High Viscosity Oil

The higher the number, the thicker the oil. This type of engine lubricant is meant for warmer climates, which for most lawnmowers is where they will see the most action.

Thick oil used in cold temperatures can lead to the engine working harder than necessary, almost like running in sand. However, higher numbers likely won’t be an issue for most lawnmowers.

Types of Oil

One of the other things you’ll see written on a bottle label is the type of oil. There are three main ones, ranging from high performance to those designed more for everyday use.

Synthetic Motor Oil

This is the highest quality oil you can buy for your engine. Chemical engineers design it to make the molecules more uniform in shape and have fewer impurities. Because of the work that goes into it, synthetic oil performs better in extreme conditions and is recommended for drivers in cold climates or heavy-duty machinery.

Conventional Oil

Less engineering goes into this oil, so it can be a bit cheaper. It also comes in various viscosity grades. However, it won’t perform as well in extreme temperatures and is recommended more for casual motor needs.

Synthetic Blend Motor Oil

As the name suggests, this type of oil is a blend of conventional oil and synthetic, placing it somewhere between the two in terms of quality. It’s a middle-of-the-road oil that provides some of the benefits of synthetic oil while being more cost-effective.

Should I Adjust Motor Oil Based on Climate?

As most lawnmowers are operated in warmer and dry weather, it isn’t necessary to change oil based on the climate. All you need to do is make sure that the viscosity grade matches the kind of weather you’re operating your lawnmower in.

For example, if you move from Mexico to Canada and bring your lawnmower with you, you’ll still only be using it in the warmer months. Any oil that isn’t overly thin should be fine.

When to Change Lawnmower Oil

How often your lawnmower requires an oil change comes down to several factors. Different types of oil are of higher quality and last longer, so if you’re using synthetic oil, you won’t have to change it as often as you would when using conventional oil.

The number of times you use the mower is also a crucial factor. Just like with the gasoline in the tank, the oil will have to be replaced more often if you mow your lawn once a week compared to once a month.

The general rule is that you should change that lawnmower oil once every year or after 50 hours of use, whichever comes first.

Final Thoughts

When considering using car oil in your lawnmower, the first step you take should be looking at the specifications of your machine. Two-stroke engines require a special oil and gas mixture that car engines don’t use, and using the wrong oil can have destructive results.

However, if your lawnmower has a four-stroke engine, you’ll be perfectly fine using the same multigrade oil that your car takes.

See also: Best Lawnmower Brands on the Market

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