SAE 40 vs 15W40- Which is Better to Pick

Motor oil is one of the most important elements in keeping your engine running smoothly and efficiently.

If you pick the wrong motor oil, then it can actually damage your engine over time. Now, the question is which is the perfect oil to use?

SAE 40 and 15W40 are two of the most popular engine oils that can be used on various vehicles. But do you know which is better SAE 40 vs 15W40?

Both these oils have their own characteristics but advantages. But there are some key differences that make one little bit better than the other. In this case, SAE 15W40 can be an ideal choice for you.

But why? In this article, we’ll try to know why pick 15W40 instead of SAE 40. So, let’s get started.

SAE 40 vs 15W40

Overview of SAE 40

SAE 40 oil is classified as a single-grade oil. It maintains a consistent viscosity across a wide range of temperatures.

Because of its high viscosity rating, it is suitable for use in high-temperature environments where thicker oil is required for adequate lubrication and protection against wear.

It is formulated to provide excellent protection for engines operating under heavy loads and high temperatures. You can use this oil in older engines that are designed to work with high-viscosity oil.

It is important to note that SAE 40 oil is not suitable for use in modern automotive engines that require lower-viscosity oils.

What We Like

Suitable for high-temperature applications

Enhanced wear protection

Cost-effective options

What We Dislike

Not suitable for modern vehicles

Overview of SAE 15W40

SAE 15W40 is a multi-grade motor oil and is designed to provide lubrication at both high and low temperatures. It is used in many types of vehicles including cars, trucks, and motorcycles.

“15W” refers to oil viscosity at cold temperatures, while “40” refers to oil viscosity at hot temperatures. “W” means winter, and “40” means summer.

It is designed to flow easily at low temperatures and provide protection at high temperatures. At lower temperatures, the oil will flow faster and reduce lubrication and friction in the engine.

At high temperatures, oil will thicken and SAE 15W40 is a multi-grade motor oil and is designed to provide lubrication at both high and low temperatures.

It is also commonly used in engines that are used in cold climates, as it can also provide protection in low temperatures. This oil is perfectly suitable for modern engine vehicles.

What We Like

Gives excellent lubrication and works against wear and tear

Suitable for modern engine vehicles

Helps to maintain fuel economy and reduce emissions

What We Dislike

A little bit more expensive than other types of oil

SAE 40 vs 15W40- Head to Head Comparison

Both SAE 40 and 15W40 are designed to lubricate engines and reduce friction. But there are several key differences between these oils that make them apart from each other.

Here we will try to share some of the major differences between SAE 40 vs 15W40.

Viscosity Grade

You surely know how important the viscosity grade is when selecting a lubricating oil for an engine. It determines the resistance flow of oil at different temperatures.

Read More About Viscosity

It plays a major role in influencing the proper lubrication and protection of engine components.

SAE 40 is a monograde oil. It has a single viscosity rating of 40°C at 100°C.

It is suitable for use in hot climates or during the summer season when the engine operates at high temperatures.

SAE 40 provides a consistent viscosity throughout its operating temperature range. This makes it ideal for engines that require a single viscosity oil.

On the other hand, 15W40 is a multi-grade oil. It combines the benefits of both a low-temperature viscosity rating (15W) and a high-temperature viscosity rating (40).

The number “15” indicates the oil’s low-temperature viscosity rating, while “40” indicates the high-temperature viscosity rating.

It means that 15W40 is better suited to handling cold weather temperatures than SAE 40. So, 15W40 is the clear winner in terms of viscosity.

Cold Weather Performance

A motor oil’s cold weather performance is an important factor to consider when deciding between SAE 40 and 15W40.

The first number in the oil grade represents the ‘W’ rating. It stands for winter grade.

This rating describes the oil’s ability to flow at low temperatures and is measured in degrees Celsius.

When comparing SAE 40 vs 15W40, the latter has a higher viscosity rating due to its ‘W40’ or ‘winter’ grade.

It means that it maintains a higher viscosity (or thickness) at colder temperatures than SAE 40.

This is why it is suitable for cold climates and provides better protection against wear when running your engine in cold temperatures.

However, this benefit comes with a tradeoff in fuel efficiency, as thicker oil reduces fuel economy.

Shear Stability

Shear stability is an important property of engine oils. It determines how well the oils can maintain viscosity and lubricating properties under high-pressure conditions.

The viscosity index improver (VII) used in multigrade oils allows them to maintain their grade when shearing forces are in service.

So, when comparing SAE 40 vs 15W40, we must look at the VII additives used in each type of oil.

SAE 40 engine oil is less likely to break down due to shearing than 15W40 motor oil because it contains no viscosity index-improving additives.

On the other hand, 15W40 motor oil contains viscosity index improvers. It can break under shearing force. As a result, performance decreases over time.

In terms of shear stability, SAE 40 is more suitable than 15W40. It contains no viscosity index improver additives and is therefore less likely to degrade under extreme operating conditions.

Fuel Economy

When it comes to fuel economy, both SAE 40 and 15W40 are in a neck-to-neck competition.

Ultimately, the one you should choose depends on what type of vehicle you have and the climate you live in.

SAE 40 is more viscous and it needs more energy to move it. But, it provides less fuel economy.

On the other hand, 15W40 is less viscous than SAE 40 and provides better fuel economy as less energy is needed to move it. it results in a lower drag on the engine due to reduced friction.

Higher temperatures require higher viscosity oils such as SAE 40. This is why engines can be adequately lubricated while running at peak performance and temperatures.

So if your vehicle is mostly used in an area with hot climates throughout the year then SAE 40 would be a better option for fuel economy.

But, if you live in an area with cold climates, then 15W40 would be a better option for you. Its lower viscosity makes it easier to work even at low temperatures.

Overall both are quite close when it comes to providing effective fuel efficiency. You can pick one which suits your needs.

Application to Use

No matter how good a motor oil is, it won’t do you any good if it’s not the right fit for your vehicle.

Unfortunately, there’s no simple answer that can determine which type of oil is better for your engine.

As SAE 40 is a single-grade oil, it maintains a consistent viscosity throughout a wide temperature range.

It is recommended for use in older vehicles or in specific applications where a higher viscosity oil is required. SAE 40 is not recommended for use in cold weather conditions. It may become too thick and cause poor lubrication during startup.

On the other hand, 15W40 is formulated to provide both cold weather and high temperature performance. It is commonly used in modern vehicles, including gasoline and diesel engines

You can also use it in heavy-duty applications such as commercial trucks and construction equipment. It offers a good balance between cold weather performance and high temperature protection.

SAE 40 vs 15W40- The Winner

Now that you know the difference between SAE 40 vs 15W40. And now you’re probably thinking which one is better to choose, right?.

There is no denying that both are pretty good quality oils. But when it comes time to choose between the two, you must keep an eye on everything.

We have already highlighted some of the key differences between these two oils. And all things considered, we put 15W40 ahead of SAE 40.

But that doesn’t mean you can’t use SAE 40. At the end of the day, it’s totally up to you which one you use. But if you want our advice, we’d suggest you go for 15W40.

Frequently Asked Questions

Q. What is SAE 40 equivalent to?

Aviation oils with a viscosity grade of 80 are equivalent to SAE 40 oil viscosity. The viscosity of these oils is 14.6 cSt @ 100°C.

Q. What is SAE 40 oil used for?

SAE 40 motor oils can be suitable for a wide variety of vehicles. Some of the notable vehicles are passenger cars, light trucks, powerboats, motorcycles, and other stationary equipment suitable for use with four-stroke gasoline engines. You can also use them for high-revving engines in small cars and light trucks.

Q. Can I use SAE 40 instead of 15W40?

While SAE 40 is a single-grade oil, 15W40 is a multi-grade oil. For this reason, SAE 40 should not be used in any vehicle that supports 15W40. Because it may damage your engine.

Q. Can I use SAE 40 instead of 5W40?

No, it’s not recommended to use SAE 40 instead of 5W40. It may not provide adequate lubrication in modern engines, particularly during cold starts, and could potentially cause engine damage.

Final Thought

You already have a better idea of these two types of oils and you can make a better decision between SAE 40 VS 15W40.

Ultimately, the best oil for your vehicle depends on your individual engine demands. Hopefully, this small effort will be helpful for all of you to pick the right oil. Thank you all.



Emon is Lubricants specialist who studied on Petroleum Engineering in UAE. He have more than 10 years experience on different kinds of lubrication including automobile troubleshooting.

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