5w40 vs. 15w40 Engine Oil: Differences and Can You Swap Them?

Knowing the right and suitable motor oil for your engine is an essential matter. Your motor oil performs an excellent function to your engine. A motor oil improves your engine performance and prevents any maintenance. 

A viscosity means a fluid’s resistance to flow. If the viscosity is high, the oil will take longer to flow into the engine than a low viscosity oil. If the temperature rises, the oil viscosity will drop. 

As a result, the motor oil will become thinner. If these additives are introduced to base oils, then they will behave like thin oil. So in this article, we’ll be talking about 5w40 motor oil and 15w40 motor oil. 

We will discuss the differences between 5w40 motor oil and 15w40 motor oil and if you can swap them? Let us get started.

5w40 vs. 15w40 Engine Oil

What Is the Difference Between 5w40 and 15w40 Oil?

5w40 motor oil and 15w40 motor oil have their similarities, and they also have their differences. Some car drivers are swapping these two motor oils, but most drivers do not because they are afraid of the consequences. So let us differentiate 5w40 motor oil and 15w40 motor oil in terms of fuel economy, hot weather, and viscosity.

Viscosity

The society of automotive engineers or the SAE and American petroleum institute or AOI provides a specific standard in measuring oil viscosity. For example, motor oil with an SAE viscosity grade of 5w40 will move like a 5w oil in low temperatures and forty in high temperatures. 

So an engine in an operating temperature, 5w40 motor oil, and 15w40 motor oil will have the same viscosity grade. However, one will become thinner and will also have a lower viscosity grade than the other.

Fuel Economy

The economic status of motor oil will depend on the consumption level and its availability in the market. For example, the 5w40 motor oils are not always available in the market. On the other hand, the 15w40 motor oil is used widely in the market because it is a multi-grade oil. 

The 15w40 motor is also cheaper because you can use it in so many engines. So it controls most of the economy. But, unfortunately, there is not so much data about their differences and similarities in fuel economy.

Hot Weather

The 15w40 motor oil is relatively thicker than the weight of seventy percent. This is because of the polymer that gets thicker to forty weight. The 5w40 motor oil is a thin oil at seventy degrees Fahrenheit, and it will be forty weight if it reaches the average operating temperature. 

This usually works in the opposite of what the public thinks. For example, most people think that the motor oil will get thinner if it gets hot. Well, it usually does, but there is the issue of polymers. 

The letter w stands for winter. It will shoot the flow rate of the motor oil if it is freezing. If the number is low, then the oil will be thin.

Can I Use 5w40 Instead of 15w40?

Yes, you can use 5w40 motor oil instead of 15w40 motor oil. This is because no engine will become damaged if the motor oil is less thick than cold. 

On the other hand, a 5w40 motor oil will be thicker also when hot. However, in choosing the right and suitable motor oil for your vehicle, you must use the motor oil and the viscosity grade recommended by your manufacturer.

Accidentally Used 5w40 Instead of 15w40: Is It Ok?

Yes, it is okay. You don’t have to worry about any significant damages or engine failure. If you lower the first number, it will give you faster oil circulation on startup. 

This is true, most especially in the cold. Your engine will then have a decrease in wear for every startup. It then flattens the viscosity curve in hot areas. 

The rule of thumb is to always check your owner’s manual for your vehicle’s recommended motor oil and viscosity grade. If it says both motor oil, then you are good to go. 

Many engines require a specific viscosity so that the engine will perform adequately. The best recommendation is to follow the recommended motor oil of the manufacturer of your vehicle.

5w40 vs 15w40 High Mileage

Mechanics are using 5w40 motor oil to support high mileage engines. This is because it is thicker under hear than any other motor oil. It also lubricated moving parts even better. 

On the other hand, using a 15w40 motor oil can be used in engines that have high mileage.

Which Is Better, 5w40 or 15w40 Oil?

In choosing the best motor oil for your vehicle, you must pick it considering the recommended motor oil of your manufacturer. This is a significant rule and a rule that everyone must follow. This will also determine the warranty of your vehicle. 

It is also essential to know that the weather will play a huge role in determining the best motor oil for your engine. For example, if you reside in a cold region, the 5w40 motor oil will be much better to use than the 15w40 motor oil because the 5w40 motor oil will ease faster and quieter in cold starts. On the other hand, if you reside in an area that is not very cold, then the 15w40 motor oil will be much better to use.

When Should I Use 5w40 And When 15w40?

The choice between 5w40 motor oil and 15w40 motor oil will depend on the winter temperature of your area. The 5w40 motor oil is much better to use in starting your engine in low temperatures. This is because the 5w40 motor oil will flow more easily in these temperatures. 

However, if the engine is also running hot, the 5w40 motor oil has a high viscosity and can protect your engine against wear and tear. The 5w40 motor oil is also preferable to use in-vehicle engines that are European vehicles with gas-powered engines.

5w40 vs. 15w40

5w40 vs. 15w40 Toyota

The recommended oil for all Toyota engines is 5w30 motor oil. The 5w40 motor oil and the 15w40 motor oil are not included in a Toyota engine’s recommended list of motor oils. You can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. 

However, if you’re in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. You must remember, though, to always refer to your owner’s manual.

5w40 vs. 15w40 Nissan

The recommended motor oil for Nissan vehicles is 5w30 and 10w30. The 5w40 motor oil and the 15w40 motor oil are not included in a Nissan engine’s recommended list. However, you can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. 

However, if you’re in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. But, again, always refer to your owner’s manual for the recommendation.

5w40 vs. 15w40 Subaru

The recommended motor oil for all Subaru engines is 0w20 and 5w30. The 5w40 motor oil and the 15w40 motor oil are not included in a Subaru engine’s recommended list. However, you can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. 

However, if you are in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. You must remember, though, to always refer to your owner’s manual.

5w40 vs. 15w40 Mazda

Almost all the vehicles and SUVs of Mazda will need 0w20 motor oil. Their lone standout might be used with some 5w30. The 5w40 motor oil and the 15w40 motor oil are not included in a Mazda engine’s recommended list. 

You can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. However, if you are in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. Always refer to your owner’s manual for the recommendation.

5w40 vs. 15w40 BMW

For all BMW engines, they are recommending 5w30 motor oil. The 5w40 motor oil and the 15w40 motor oil are not included in a BMW engine’s recommended list of motor oils. You can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. 

However, if you are in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. You must remember, though, to always refer to your owner’s manual.

5w40 vs. 15w40 Ford

According to the 2020 ford owner’s manual, almost all of their engines must be using a 5w30 motor oil or 0w30 motor oil. The 5w40 motor oil and the 15w40 motor oil are not included in a Ford engine’s recommended list of motor oils. However, you can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. 

However, if you are in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. But, again, always refer to your owner’s manual for the recommendation.

5w40 vs. 15w40 Chevrolet

For Chevrolet, the recommended oil is 5w20, 5w30, or 10w30 in some engines. And according to the owner’s manual of a 2020 chevy, they would recommend 0w20 motor oil or 5w30 motor oil. Therefore, the 5w40 motor oil and the 15w40 motor oil are not included in the recommended list of motor oils to be used in a Chevrolet engine. 

You can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. However, if you are in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. You must remember, though, to always refer to your owner’s manual.

5w40 vs. 15w40 Jeep

The recommended viscosity for jeep vehicles is 0W20, 5W20, 5W30, or 10W30. The 5w40 motor oil and the 15w40 motor oil are not included in the recommended list of motor oils to be used in a Jeep engine. However, you can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. 

However, if you are in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. Again, always refer to your owner’s manual for the recommendation.

5w40 vs. 15w40 Volkswagen

Their recommendation is only 5w30 and 0w20. The 5w40 motor oil and the 15w40 motor oil are not included in a Volkswagen engine’s recommended list of motor oils. You can use 5w40 motor oil in starting your engine in low temperatures because it will flow more easily. 

However, if you are in an area with a below-freezing temperature or an older car, it would be better to use 15w40 motor oil. You must remember, though, to always refer to your owner’s manual.

Summary

In summary, 5w40 motor oil and 15w40 motor oil are sometimes being swapped by car drivers. If you can avoid doing so, then you should because you can swap them both. 

However, the right thing is to refer to your owner’s manual for the recommended motor oil. Then, your manufacturer knows what the best motor oil for your vehicle is.

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more