SAE 30 vs SAE 40 is a debate that can be a bit puzzling to resolve for many homeowners, especially when they have both at hand. They end up confused when it comes to using the right engine oil for the lawn mower.

Comparison of SAE 30 vs SAE 40

If you’re also wondering which one is better, we’ll help you get right to the answer.

Features SAE 30 SAE 40
Viscosity Less viscous at high temperatures More viscous at high temperatures
Uses Smaller engines Larger engines
Benefits Improved engine protection Reduces maintenance
Limitations Not ideal for larger engines Not ideal for smaller engines

What Are The Key Differences Between SAE 30 and SAE 40?

The key difference between SAE 30 and SAE 40 is that the SAE 30 is used for smaller machines, such as lawnmowers, but the SAE 40 is one that is used for bigger machines such as cars. In addition, SAE 30 has less count than SAE 40.

It can be pretty tempting to just get whatever oil we have on hand and use it on our small engines. After all, it’s better than making a trip to the store to buy a more specific grade oil. And sometimes, it does work out. But then again, did we do the right thing?

– Viscosity Values

This is the biggest factor when it comes to both oils. SAE 30 has a lower viscosity when it comes to oil grades. SAE 40, evidently, has a higher count.

Viscosity Values of SAE30

To elaborate further, when the oil used is too thick, it does not flow easily through the mechanical parts, and this can result in increased wear on the moving parts. Additionally, it can lead to reduced fuel efficiency.

When the oil is too thin, it will not be able to provide adequate lubrication to the right moving parts. This can lead to increased wear and tear. Eventually, it can lead to engine damage. Even using SAE 30 or SAE 40 as a hydraulic oil can be problematic.

Since they are not formulated specifically for use on hydraulic systems, your machine could experience damages that require costly repairs or replacement. On the other hand, when you are using the recommended viscosity for specific engines is always advisable, especially when specifically stated in the owner’s manual from the manufacturer. This can reduce engine damage while ensuring your equipment’s longevity.

– Oil Uses

SAE 30 is ideal for small engines, such as lawnmowers. On the other hand, SAE 40 is better suited for larger engines, such as farm equipment, commercial vehicles, and passenger cars.

– Benefits

When SAE 30 is used in a lawnmower, lubricates the engine very well and can last a long time. SAE 40 can be used on lawnmowers as a temporary solution, but it is not recommended since the oil grade is not approved by the manufacturer. This is important, especially if your equipment is still under warranty and may be subject to certain conditions set by the manufacturer.

SAE 30 Properties

SAE 30 is a monograde oil that is used mainly at temperatures above the freezing point, because it will stay functional. SAE 30 oils do not possess excellent cold flow properties, making them inadequate for cold temperatures.

SAE 30 Properties

These oils can only be used during the spring, summer, and autumn seasons.

– Viscosity

The acronym SAE refers to the Society of Automotive Engineers, which created a scale to rate the viscosity of certain compounds. The scale starts with zero as the least viscous and goes up to 60 as the most vicious. The 30 in SAE 30 refers to a viscosity level that sits in the middle of the scale.

– Specific Uses

The SAE 30 motor oil is typically used for small air-cooled engines. These include lawnmowers, small tractors, and chainsaws. Thinner oils tend to perform better in cold weather, especially when starting smaller engines.

In short, the usage of this oil should be handled with the right requirements, especially in the right machines, because that is when you will see the machine working at its utmost potential.

– Benefits

SAE 30 oils tend to provide improved protection and resistance against engine wear and high-temperature oxidation deposits. While it is primarily targeted for use in small engines, some vintage cars require engine oils with low-additive levels and high to medium levels of viscosity.

– Limitations

SAE 30 is only ideal for temperatures that do not go beyond freezing since it is rated for hot viscosity, which is why this oil, in particular, will not be as greatly functional as it should be when the weather gets colder than usual.

When used in larger engines, such as passenger cars, it may work temporarily, although it can lead to complications.

This means that the SAE 30 will have a viscosity peak of 212 degrees Fahrenheit. Once the temperature goes past this figure and reaches 250 to 260 degrees Fahrenheit, there is a high probability that the engine will overheat and may become damaged.

SAE 40 Properties

SAE 40 is a monograde motor oil based on mineral oil formulations with very minimal additives. During operation, it tends to form a fine oil mist that lubricates all points that are not applied through oil splash lubrication.

SAE 40 Properties

The engine oil has strong adhesive powers guaranteeing excellent lubrication instantly.

– Viscosity

Similar to the SAE 30 grade oil, the SAE 40 is graded according to hot viscosity levels by the same group of automotive engineers. It sits a bit higher at 40, which means it is slightly thicker than SAE 30. The SAE 40 is more used for vehicles and bigger engines, because of its thick viscosity.

– Specific Uses

SAE 40 motor oils are suitable to use in high-revving gasoline engines with four-stroke mechanisms. These include light trucks, passenger cars, and even powerboats.

Motorcycles and other stations or mobile equipment are also suitable for SAE 40 engine oils, and this is due to its texture. This is due to the SAE 40 being able to hold up at higher temperatures while lubricating more powerful motors.

– Benefits

There are two main benefits to using SAE 40 motor oils; in parallel to this, the first is that it ensures vehicle availability and engine durability. SAE 40 oils protect from engine wear and maintain engine cleanliness.

On another note, you must also keep in mind how the 40 oils reduce maintenance and downtime since it maximizes oil drain intervals. This allows vehicles to stay on the road for a lot longer, and it would increase the durability of the machine it is being used in and the oil.

– Limitations

While SAE 40 oils are recommended for many larger engines, not all are ideal. These include engines where specific classified oils are required for use, gas-fueled engines, and certain systems that use diesel engines.

Similar to the SAE 30, this motor oil is not recommended for engines that need to start in cold temperatures. While it is a general recommendation, some motorcycles and machines that use the diesel engine system have been able to utilize the SAE 40.

For lawnmowers, the use of SAE 40 is not encouraged. While the oil viscosity is not that vast from the SAE 30 oil, the thicker motor oil can eventually strain the lawnmower’s engine.


1. Can You Substitute SAE 40 With SAE 30 in Lawnmowers?

Yes, the SAE 40 motor oil can be used in place of SAE 30. However, its usage should not be regular or even frequent.

Can You Substitute SAE 40 With SAE 30 in Lawnmowers

Using oils other than the recommended grade can result in engine deterioration and damage. Plus, it can possibly void any product warranty granted by the manufacturer.

2. Can You Mix Both SAE 30 and SAE 40 for Lawnmower Use?

No, it is not recommended to mix SAE 30 with 40. Regular use of mixed oils can result in engine degradation and eventual damage. This can also lead to repairs, which can end up more costly than using the right synthetic oil recommended for your engine.


Using the right oil for your machine’s engine is important, especially if you’re looking to keep it well-maintained and working optimally. Here are a few reminders when choosing the right:

  • Use the right oil for your machine, equipment, or engine.
  • Substituting one oil for the other may lead to damage or nullification of warranties.
  • Avoid mixing different oils to avoid damaging your equipment, machines, or engines.

Now that we’ve covered everything for you, we’re sure you’ll know what to do when it comes to caring for your lawnmower. With this abundant knowledge, you will not let your machines down, because you know the significant differences between both oils. Check out the differences between SAE 30 and 15W40 motor oils as well.

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