Can I use 10w40 Oil in My Lawn Mower?

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There are different grades of engine oil. Each grade is argued to be suitable for particular engines. You could run out of recommended oil some time and need a quick alternative.

Suppose all you have in the house is the 10w40 oil for your vehicle. Should you use it for your lawn mower? 

What makes this oil different? Let’s talk about that. Then, you can make an educated choice on whether or not you want to use it for your mower.

Lawn Mower Oil Recommendations

Using the wrong oil in your lawnmower may damage it irreparably. You might not see the engine blow up, but it is likely to wear off and stop working over time,  earlier than it should.

The commonest recommendations for lawn mowers are the SAE 30 or 10w30 engine oil.

Types of Engine Oil for Lawn Mowers

Small engine oils or motor oils may be used in lawnmowers. If you think that both types of oil are the same. Don’t feel embarrassed if you do, I used to think so too.

An engine oil is designed for high temp environments in air-cooled engines. You get motor oil from gas stations and they are used for larger motors such as automobiles and riding mowers.

Mineral oil vs Synthetic Oil

Mineral oil is the least refined engine oil. It is cheaper but offers poor protection against heat. It is also inefficient in cold temperatures. Mineral oil is consumed at a faster rate when used at high temperature and requires a frequent refill.

Synthetic oil offers better and faster lubrication to the engine. It is also better at collecting dust and debris associated with mowing.  Full synthetic oil maintains optimal function under different temperatures and stress conditions.

As synthetic oil is costly, a great alternative might be semi-synthetic oil or a synthetic blend oil. It is produced by the addition of a small amount of full synthetic oil to mineral oil. 

While it does not offer the full protection of synthetic oil, synthetic blend oil has improved resistance against high temperatures and stress. 

Grading of Engine Oil

According to the society of automotive engineers (SAE), engine oils are graded based on viscosity. Viscosity is the degree to which an oil resists flow under certain conditions. That is the size of the internal friction of a fluid. 

Highly viscous oils resist flow when sheared by mechanical components in motion. The viscosities of oils are observed at room temperature and operating temperature.

Some internationally used engine oil grades are 0W-20,0W-30,OW-40, 5W-30, 5W-40, and 10W-40

In the code for oil grades, ‘W’ stands for ‘winter’. It represents the starting temperature.  The number preceding ‘W’ is the viscosity of the oil in cold temperatures. The number following ‘W’ is the viscosity of the oil at normal operating temperature.

Here’s an example: 

A  0W40 oil will have 0 viscosity (be very thin) at the starting temperature when the engine is cold. The viscosity of the oil becomes 40 (thicker) when the engine is at the operating temperature.

Based on the grading, a 10W30 has less viscosity (is thinner) at operating temperature than a 10W40 oil. Therefore, it will flow better at that temperature. 

Now, what does all of this mean for you and your mower? The thing is, oils with higher viscosity move more slowly when the engine is operated. 

This can lead to large oil temperatures and increased drag. Simply put, the engine would not work efficiently. 

In the same vein, oils with low viscosity can lead to excessive contact between metallic parts of the engine leading to friction and wear. Therefore, the key is choosing an  oil with the right level of viscosity for your engine type.

What is 10w40 Oil?

 As I mentioned earlier, 10W40 oil has a 10 weight performance or viscosity in winter, and 40 weight performance under the temperature of an operating engine. It is a multigrade detergent oil commonly used in vehicles.

10W40 vs 10W30/ SAE 30

The major difference between 10W40 and 10W30 is that 10W40 oil will stay more viscous than 10W30 oil, when hot. However, the difference in operating temperature viscosity is small.

SAE 30 maintains a single weight or viscosity at every temperature.  Meanwhile, 10W40 is a multigrade oil and is thinner when cold. This means you might have it easier starting the engine with a 10W40 on a cold day than an SAE 30.

However, being a multigrade oil, a 10W40 oil will be consumed more quickly than SAE 30. Therefore, the SAE 30 will last longer than 10W40, saving you money in the long run.

Furthermore, 10W40 performs better in warm environments. SAE 30 will be too thick under very cold conditions. At warm temperatures, there’s a less significant difference between the operation of SAE 30 oil and 10W40 oil.

10W40 oil has a poor American Petroleum Institute (API) rating for small engines, compared to 10W30, or even SAE 30. They are better used in large mowers, especially those with pressurised oiling systems. 10W40 is unlikely to cause major damage to a lawnmower engine, especially over short term use.

How to Choose Best Oil for Your Mower

Now, let’s go through factors that are important to consider when choosing an oil for your mower:

The Temperature of Your Environment 

In cold environments, you want to use oils that have low viscosity in winter. An SAE 5W-30 oil is recommended. SAE 30 is commonly used in warmer climates.

SAE 10W-30 oil is preferred in areas where the temperature fluctuates between 0°c and 100°c. Vanguard 15W-50 is also good under widely varying temperatures

Mower Size

SAE 30 is most commonly used for small engines. Larger mowers like the zero turn mowers for 3 acres are more likely to work well with 10W40 oil.

Mower Engine

There are two-cycle and four-cycle engines. Two-cycle engines cannot use the same oil as your vehicles. They require less viscous oils with APR gradings SF, SG, SH or SJ. However, four-cycle engines have separate compartments for oil and gasoline and can use regular motor oils 

Mower Type

Some manufacturers recommend specific oils for the type of mower. If your mower has an operator’s manual, you may have to check the oil recommendation. If not, you can check the website of the manufacturing company for some information.

Here’s some advice: It is important to choose top quality detergent oils marked as ‘For service SF, SG, SH, or SJ’.

When To Change Your Mower Oil


It is helpful to read your mower manual to know when to change the engine oil. I do not have a manual for my mower, so I can totally relate if you don’t.

For a new mower, you may need to change the oil after it works for up to 5 hours. 

For old mowers, oil is changed between 20 hours to 50 hours depending on the size. You could also change the engine oil once every spring or summer before your first mow, or annually.

You may need to change the oil more often when the mower works harder than usual. For instance mowing a soft terrain, wet grass or under unusually hot weather. To be doubly sure, use a dipstick or a clean cloth to check the level of oil.

Briggs and Stratton say oil capacity in walk-behind mowers is usually 15 ounce or 18 ounces. For riding mowers, the oil capacity is 48 oz or 64oz.

How to Change Lawn Mower Engine Oil

How to Change Lawn Mower Engine Oil

Warm Up The Engine

Start your lawn mower engine for about a minute. Then turn off the engine. Unplug the spark plug wire to prevent the mower from accidentally restarting. Tidy dipstick shaft and drain the plug areas. Finally, remove the dipstick

Drain Oil

The first thing you want to do is ensure the spark plug is facing up by propping up the mower deck. Put your oil-collecting container under the mower. Unscrew the oil plug in an anticlockwise manner. Drain the oil into a container.

Replace the Oil Filter


Remove the oil filter by twisting it anticlockwise. Clean the filter if necessary. Next, ensure that the oil gasket has no dirt or debris. Thereafter, place in the new oil filter and screw it into position. Use a wrench to tighten it.

Refill the Engine Oil

Keeping the oil capacity of the mower in mind, pour adequate oil. Clean the dipstick again and reinsert it into the dipstick shaft. Bring it out again to check if the oil is at the right level.


  • Always drain oil into an oil safe container
  • In case you forget to use the dipstick, signs like white or grey smoking from the lawnmower could suggest that the engine has too much oil. 
  • Using synthetic oil does not alter the required frequency of oil change.