15w40 vs. 20w50 Engine Oil: Differences and Can You Swap Them?

A task as simple as choosing the suitable motor oil for your engine can be challenging. A motor oil seller might know a lot about these motor oils, but the only one that knows the recommended motor oil for your engine is the manufacturer of your vehicle. With that, you should refer to your owner’s manual for the recommended motor oil. 

A lot of car drivers don’t know about the recommended viscosity for their engines. They are also overwhelmed with their choices. When it is time to pick the right motor oil for their engine, many car drivers get confused with their choices because there can be many different types of motor oil in the market.

So in this article, we’re going to talk about 15w40 motor oil and 20w50 motor oil. We will be talking about their differences and if you can swap the two of them. Let us get started.

15w40 vs. 20w50 Engine Oil

What Is the Difference Between 15w40 and 20w50 Oil?

Let us learn about the differences between 15w40 motor oil and 20w50 motor oil. We will be comparing them in terms of fuel economy, hot weather, and viscosity.

Viscosity

The viscosity of the motor oil plays a big part in deciding if a specific engine will stand out among other engines or not. Therefore, the 15w40 motor oil and 20w50 motor oil have their specific categories based on some aspects that are the same. As an example, the 15w40 motor oil has fifteen (15) as its viscosity rating. 

It has forty (40) for low and high-end temperatures. On the other hand, the 20w50 motor oil has twenty (20) or fifty (50) viscosity ratings. 

These motor oil viscosities will define the potential of lubrication in cold and hot temperatures. So it is essential to know and understand the best vehicle for specific motor oil and vice versa.

Fuel Economy

The 15w40 motor oil and 20w50 motor oil can both provide good fuel economy. Motor oils nowadays are already equipped with the ability to improve the engine’s fuel economy. You have to stick with what is recommended by your engine so that you will reap the full benefit of an improved fuel economy.

Hot Weather

The 15w40 motor oil and 20w50 motor oil are both thick. As a result, this makes them a perfect and ideal choice for a high temperature. Suppose you have a heavy-duty vehicle and maintain a high operating temperature, or it might run entirely in a high-temperature climate. 

In that case, both of these motor oils will be a perfect option that you can use. But to choose between 15w40 motor oil and 20w50 motor oil, there is one thing you must always consider. Always refer to the recommended motor oil stated in your owner’s manual.

Can I Use 15w40 Instead of 20w50?

This will depend on several things. First, the determining factor of which motor oil should be used will depend on two factors. You should be familiar with this to know if you can use such motor oil or not in the future. 

Now, the first factor that you should consider is the temperature. After the temperature, you should consider the number two. The second factor that you must consider is viscosity. 

So again, before using any motor oil for your engine, you should first know what your manufacturer would recommend. The recommendation of the motor oils for your vehicle will depend on two factors.

Accidentally Used 15w40 Instead of 20w50: Is It Ok?

Yes, it is okay in the sense that you will not have significant and severe problems to encounter. However, if you are worried that there might be some damages or failures in your engine, do not fret because it is okay. The 15w40 motor oil and 20w50 motor oil can be used depending on the car driver’s risk-taker. 

This means that the 15w40 motor oil and the 20w50 motor oil must only be used if recommended for your engine. So if you have accidentally used 15w40 motor oil, it is okay, but if it is not recommended for your owner’s manual, it would be better to do an oil change.

15w40 vs 20w50 High Mileage

Using a 15w40 motor oil can be used in engines that have high mileage. On the other hand, the 20w50 motor oil is used more in racing engines and not on high mileage engines. 

High mileage engines are running very hot and need heavy load operation. 20w50 motor oil is not for those vehicles that are driven daily. 

Which Is Better, 15w40 or 20w50 Oil?

If you have a new engine that uses 15w40 motor oil, then the best motor oil is 15w40 motor oil. But if you wore down three hundred thousand (300,000) miles engines and it is using 15w40 motor oil, then the 20w50 motor oil might be good because it has thicker lubrication in there. It will also stick with your bearing, and it can be around your internal moving parts and more protection against wearing out. 

The 15w40 motor oil and the 20w50 motor oil have different effects on a specific engine because they have different weights and viscosity. This will also depend on the recommendation of your owner’s manual.

When Should I Use 15w40 And When 20w50?

The 15w40 motor oil is ideal for heavy-duty vehicles and gasoline engines that demand SJ, API SL, and SM grading. So always make sure that the motor oil is suitable for your vehicle. Not all trucks and buses are suitable for thicker motor oils. 

The 20w50 motor oil is thick, and it is preferable to use in heavy-duty engines, and it is less efficient in cold regions than the 15w40 motor oil. So always refer to your owner’s manual.

15w40 vs. 20w50

15w40 vs. 20w50 Toyota

The recommended oil for all Toyota engines is 5w30 motor oil. The 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. 

For the 20w50 motor oil, you can use it in warm climates if the temperature is high. The 15w40 motor oil is a multi-grade oil, and it can work fine in summer and winter.

15w40 vs. 20w50 Nissan

The recommended motor oil for Nissan vehicles is 5w30 and 10w30. The 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. For the 20w50 motor oil, you can use it in warm climates if the temperature is high. 

The 15w40 motor oil is a multi-grade oil, and it can work fine in the summer and winter. However, the best decision is to refer to your owner’s manual.

15w40 vs. 20w50 Subaru

The recommended motor oil for all Subaru engines is 0w20 and 5w30. The 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. 

For the 20w50 motor oil, you can use it in warm climates if the temperature is high. The 15w40 motor oil is a multi-grade oil, and it can work fine in the summer and winter seasons. But, again, look for your owner’s manual for the recommended motor oil.

15w40 vs. 20w50 Mazda

Almost all the vehicles and SUVs of Mazda will need 0w20 motor oil. Therefore, the 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. 

For the 20w50 motor oil, you can use it in warm climates if the temperature is high. The 15w40 motor oil is a multi-grade oil, and it can work fine in the summer and winter seasons.

15w40 vs. 20w50 BMW

For all BMW engines, they are recommending 5w30 motor oil. The 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. 

For the 20w50 motor oil, you can use it in warm climates if the temperature is high. The 15w40 motor oil is a multi-grade oil, and it can work fine in the summer and winter seasons.

15w40 vs. 20w50 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 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. For the 20w50 motor oil, you can use it in warm climates if the temperature is high. 

The 15w40 motor oil is a multi-grade oil, and it can work fine in the summer and winter seasons. However, the best decision is to refer to your owner’s manual.

15w40 vs. 20w50 Chevrolet

For Chevrolet, the recommended oil is 5w20, 5w30, or 10w30 in some engines. The 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. For the 20w50 motor oil, you can use it in warm climates if the temperature is high. 

The 15w40 motor oil is a multi-grade oil, and it can work fine in summer and winter. But, again, look for your owner’s manual for the recommended motor oil.

15w40 vs. 20w50 Jeep

The recommended viscosity for jeep vehicles is 0W20, 5W20, 5W30, or 10W30. The 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. 

For the 20w50 motor oil, you can use it in warm climates if the temperature is high. The 15w40 motor oil is a multi-grade oil, and it can work fine in the summer and winter seasons.

15w40 vs. 20w50 Volkswagen

Their recommendation is only 5w30 and 0w20. So the 15w40 motor oil and the 20w50 motor oil are not on the recommended list, but if you want to, you can use them for your engine but be prepared for some risks if there are any. 

For the 20w50 motor oil, you can use it in warm climates if the temperature is high. The 15w40 motor oil is a multi-grade oil, and it can work fine in the summer and winter seasons. But, again, look for your owner’s manual for the recommended motor oil.

Summary

In summary, people interchange 15w40 motor oil and 20w50 motor oil. Car drivers are also confused if it is right to swap them both and if it is okay.

Both 15w40 motor oil and 20w50 motor oil have their differences and their similarities. Therefore, the best option is to always refer to your owner’s manual for the suitable and recommended motor oil for your engine.

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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