Updated at: 17-03-2022 - By: micdot

It is critical that you use the engine oil recommended by the manufacturer if you want your car to run smoothly. So many individuals have inquired as to whether 15w40 and 5w40 oil can be mixed. You’ve come to the right place if you’re looking for an answer. Is it possible to use 15w40 and 5w40 oils together? Yes, however it’s not a good idea to do so. Despite the fact that there are no major drawbacks to this pastime, it is nevertheless not recommended for people to engage in it.

The public appears to be split on this issue. For instance, about half of those polled said it’s a bad idea to combine two types of motor oils that have different weights and viscosities. Some people, on the other hand, believe that blending two different motor oils, even if their viscosities and weights are vastly different, is acceptable. Because they feel that mixing it can cause considerable damage to the vehicle and lead to engine failure, several individuals avoid doing so. It is improbable that an engine will fail if two different viscosities and weights of oil are mixed together. However, this does not mean that you may just combine 15w40 oil with 5w40 oil. The viscosity and weight of these two oils are vastly different. Since there are so many misunderstandings, it’s important to know what happens if you combine 15W-40 and 5W-40 motor oil in your vehicle. It’s also important to find out if you may blend 15w40 and 5w40 oil in your vehicle. Everything you need to know about combining 15w40 and 5w40 oil is covered in this article. So without further ado, let us begin.

Can I Mix 15w40 and 5w40 Oil?

No, you can’t mix 15w40 with 5w40. When it comes to 15w40 and 5w40 oil mixtures, there are merely guidelines and no hard and fast regulations. As a result, even if your owner’s handbook advises against combining 15w40 and 5w40 oil, you are free to ignore that advice. So, if you’d like to combine 15w40 and 5w40 oil, you can do so. Mixing 15w40 oil with 5w40 oil, on the other hand, is not suggested or acceptable for everyone. The conundrum is that it isn’t technically against the law.

Because of this, car owners have the option of combining them or not, as they see fit. However, you must also be mindful of the considerable variations between the two oils you will be blending. They differ in weight and viscosity, as well as in their density. You can safely combine 15w40 and 5w40 oil as long as you are aware of the differences.

Can You Add 15w40 to 5w40 Oil?

Add 5w40 to your 15w40 if the present oil is thin and you have no other option but to change the motor oil. It’s better to just use the same amount of oil you’re already using, but that isn’t always an option. However, you are free to use a different oil if you so like. There is no evidence to support the claim that mixing 15w40 with 5w40 will result in catastrophic engine failure. That’s all there is to it.

Can You Add 5w40 to 15w40 Oil?

Adding 5w40 to your 15w40 is fine. Adding a different oil to the current oil isn’t optimal, and it’s not a good idea to do it. You can, however, add them if you must or if you so like. In the event that the oil in your car isn’t specifically designed for it, you may always get an oil change just to be safe.

Is It Ok To Mix 15w40 and 5w40 – Possible Downsides?

It is not suggested to mix two motor oils of differing viscosity and weight. Even so, you can still do it and combine the two. There are a lot of people who mix and match these two things. Because the answer to this question can be either yes or no, you may be perplexed. To put it another way, some individuals think it’s fine to blend 15w40 with 5w40 oil, while others think it’s a bad idea altogether. Here, you must rely on the advice of others who have already gone through the same situation and can speak to their own experiences.

The only drawback is that your vehicle’s warranty may be voided as a result. If your warranty has expired, you can use a mixture of 15w40 and 5w40 oil. However, the most important thing to remember is the dangers of combining different types of oils. Changing your motor oil is something you should avoid at all costs. Instead, stick with one kind of motor oil at a time. The likelihood of engine or component failure is low.

What Happens if You Mix 15w40 and 5w40 Oil?

No harm will be done to your vehicle’s engine or other parts if you mix 15w40 with 5w40 oil. It’s possible that you’ll only get the benefits of one motor oil instead of the full complement. As a result, if you want to reap the benefits of motor oil, don’t dilute it with anything else. In the tank, these oils will not mix, and they will continue to travel in their own independent directions. So, if we’re talking about engine failures and major damage to the vehicle, this is a highly unlikely situation. When 15w40 and 5w40 oils are mixed, no one has ever reported any negative effects.


Some car owners are mixing their own oil, despite the fact that it’s not suggested. People are free to do so if they choose to do so. No serious damage to the engine is possible as a result of this incident. So many individuals are experimenting with it.