Can You Mix 15w40 and 5w40 Oil? (Explained!)

Using the right and recommended motor oil for your engine is vital for the performance of your vehicle. This is why many people have been asking if they can mix 15w40 oil and 5w40 oil. If you want to know the answer, you are on the right page.

So can you mix 15w40 oil and 5w40 oil? The answer is yes, but this act is not recommended. There are no significant problems with this activity, but it is still never advised for people to do it.

When it comes to this question, the public is divided. For example, half the people would say that you should not mix two motor oils with different weights and viscosities. However, some people will also say that it is okay to mix two motor oils even though they have different viscosity and weight.

Some people are also not mixing it because they believe that such activity can cause significant damage to the vehicle and cause failure to the vehicle’s engine. In reality, though, engine failure is unlikely in mixing two oils with different viscosity and weight. But it does not mean that you can just freely mix 15w40 oil and 5w40 oil.

Both of these oils are different in terms of their weight and their viscosity. Because of these confusions, you need to know what would happen if you mix 15w40 oil and 5w40 oil. You should also know if you can indeed mix 15w40 oil and 5w40 oil.

This article will talk about everything there is to know about the mixing of 15w40 oil and 5w40 oil. So without further ado, let us get started.

Table of Contents

Can I Mix 15w40 and 5w40 Oil?

Yes, you can mix 15w40 oil and 5w40 oil. However, there are only recommendations and not rules when it comes to the mixing of 15w40 oil and 5w40 oil. This means that if your owner’s manual would recommend not mixing 15w40 oil and 5w40 oil, then you still have the choice to either follow that recommendation or not.

So, in this case, if you want to mix 15w40 oil and 5w40 oil, then you can mix them. However, you must remember that mixing 15w40 oil and 5w40 oil is not recommended and advisable for everyone. The tricky thing is that it is not prohibited.

This is why car owners still have the choice to mix them or not. However, you also need to be fully aware that the two oils you will be mixing have significant differences.

They are different in terms of their weight and also in terms of their viscosity. So if you are fully aware of these differences, you are good to mix 15w40 oil and 5w40 oil.

Can You Add 15w40 to 5w40 Oil?

If the current oil is shallow and you have no other choice but to pour different motor oil, you can add 5w40 to your 15w40. But, of course, the ideal thing to do is only to add the motor oil the same as your current motor oil.

However, it is not prohibited to add a different oil. No statement says adding 15w40 to your 5w40 causes major engine failure and problems. And for that, you are good to go.

Can You Add 5w40 to 15w40 Oil?

Yes, it is okay to add 5w40 to your 15w40. But, again, you need to know that adding a different oil to the current oil is not ideal, and it is not recommended.

However, if you have no choice and want to, you can add them up. If you want to be on the safe side, you can always have an oil change if already available motor oil is intended for your vehicle.

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

Mixing two motor oils with different viscosity and different weights is not recommended. But you can still do it, and you can still mix the two of them. A lot of car owners have been mixing the two of them.

You might just be confused because this question is answered by yes and no. It means that there are people who believe that it is okay to mix 15w40 oil and 5w40 oil, and there are people who believe that it is not okay to mix 15w40 oil and 5w40 oil. This is where you have to trust your instinct and base your decision on those who have already done the thing and share their experience.

The only possible downside that is close to happening is that your vehicle’s warranty can be voided. If you are out of your warranty, it is okay to mix 15w40 oil and 5w40 oil. But, again, the most important thing to know is the risks you have to take upon mixing two different oils.

You have to be fully aware that it is not recommended and that the ideal thing is to stick with just one motor oil at a time. Engine failure or component damage is improbable.

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

If you mix 15w40 oil and 5w40 oil, nothing significant will happen to your vehicle’s engine and components. The worst that can happen is that you will not get all the benefits of one motor oil because you have mixed two of them. Therefore, remember you want to enjoy the benefit of motor oil; you must not mix another oil into it.

Inside the tank, these oils will not blend, and they will still go separately. So if we will talk about engine failures and some significant damages to the vehicle, then this is a pretty unlikely scenario. Nobody has ever reported that they have encountered harmful effects when mixing 15w40 oil and 5w40 oil.