Can You Mix Motor Oil Weights? (Explained!)

Mixing motor oil with different weights has opened a lot of questions about its safety and compatibility. If you have the same questions, stay for a very informative read.

So can you mix motor oil weights? Mixing motor oil weights is not recommended, but a few viscosity grades can be mixed because they are compatible. But if you mix them both, you will now have a different viscosity level, which is not good because you have to maintain a certain viscosity level in your motor oil, and that is what your vehicle’s engine will require.

Before proceeding with a more in-depth explanation, let us discuss first what is an oil weight. If we will talk about oil weights, it means the viscosity of the motor oil. When we say viscosity, it means the flow of the oil at a specific temperature that it is in. 

This question is very common because there are situations when you have no choice and that you have to mix two motor oils with different viscosity. This is why everyone needs to know whether you can mix motor oil with a certain viscosity level with another motor oil with a different viscosity level. 

Some people may have already done this, and they might think that their vehicle and its engine are still doing fine, but you do not see the effect it has in the long run. So now, we will know everything there is to know about mixing motor oil weights. Let us get started.  

Can You Mix Motor Oil Weights

Is It Ok To Mix Different Weights Of Motor Oil?

It is never recommended to mix two motor oils with different weights or viscosity. But there can be some motor oils with certain viscosity levels that can be compatible and suitable to mix with another. It would help if you took note, though, that they must have the same motor oil brand. 

Each motor oil manufacturer has different ways of formulating their motor oil, and they are also using different technologies and machines. With these, each motor oil brand will have different products of motor oil. Therefore, it is essential to mix motor oil if you will with the same motor oil brand. 

The rule of thumb on this is not to do this. It is not recommended for a reason. If you find motor oils with the same brand and viscosity and mix up, it will create another viscosity level. For example, let us talk about 10w30 and 5w30. 

The 5w30 is thinner and lighter than the 10w30. Therefore, the 10w30 has a higher viscosity when compared to the 5w30. So if you mix these two, they can be mixed. 

But you must not if you can avoid it. Mixing two motor oils with different viscosity is not a guarantee that it will not do badly with your engine.

What Happens If You Mix Different Weight Oils?

Mixing two motor oils with different weights is not recommended. Mixing two motor oils with the same viscosity is already not recommended. It is with much more restriction if it is two motor oils with different viscosity. 

The viscosity is referring to the thickness of the motor oil. A specific vehicle is requiring a specific level of viscosity. If you put the wrong motor oil because it has the wrong specific viscosity level, your vehicle and vehicle’s engine can be compromised. 

Your engine can get damaged. So now, if you mix two different motor oil with different thicknesses, there might occur a shift in the viscosity level of the oil. The oil can become thicker, or it can become thinner. 

With that, your vehicle will be jeopardized. Talking about the weight of the motor oil does not refer to the actual weight of the motor oil; you need to consider and know its viscosity. Viscosity refers to the thickness of your motor oil. 

Your vehicle and its engine are requiring a specific level of viscosity. If your viscosity level is shifted because you have mixed another motor oil with different viscosity, your engine will accept the results. With that, it is essential not just to choose any motor oil. 

You must find your owner’s manual, and you must read your owner’s manual. You will know how much viscosity you will need to power up your vehicle in the owner’s manual. The viscosity came from the society of automotive engineers, or they are better known as SAE. 

A viscosity level is assigned to each motor oil. So if a motor oil has a high viscosity number, it means that the motor oil is thicker. It would also mean that the motor oil can be able to move around gradually. 

The viscosity also means how the motor oil will coat the vehicle’s engine components. It will also protect the moving parts of the vehicle against heat and friction.  

What Is The Correct Way To Mix Different Weight Oils?

Mixing different weight oils is not recommended. Therefore, the correct way of mixing it up is not something that has a piece of accurate and precise information. But if you mix different oil weights, make sure that you are using the same motor oil brand. 

Even drag racers sometimes mix up two different motor oils and different brands to create their viscosity for trivia. But even if you know that some people are already doing the mixing, it is not recommended, and it is not simple. You will have to learn so much. 

There are possible complications that will arise if you mix two motor oil with different weights or viscosity. So with that, it is never recommended to mix it. So the rule of thumb is to forget this and stick to one motor oil and one motor oil brand.


In summary, oil weights refer to the viscosity of the motor oil. It means the thickness of the motor oil. Certain vehicles require a specific type of viscosity level for the motor oil. 

Suppose you will mix one with another motor oil and with different viscosity. In that case, you can create another level of viscosity that is not recommended and suitable for your vehicle’s needs.



Image credits – Canva

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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