Can You Mix 5w30 and 10w40 Oil? (Explained!)

People are confused about whether you can mix 5w30 and 10w40 oil. Some car drivers are already doing the mixing, and some car drivers are avoiding it because they do not know the consequences of such mixing. If you wish to know more about this matter, this article is for you.

So can you mix 5w30 and 10w40 oil? Yes, you can mix up 5w30 and 10w40, but you might not enjoy the full benefit of the two motor oils that you have mixed.

Mixing two motor oils with different viscosities and weights stops some car drivers because of their differences in terms of viscosities and weight. However, if the activity is dangerous, why are there so many car drivers already doing the act? 

These car drivers have reported no danger and failure on their engines and their vehicles. So if you wish to know more about his matter, stay and keep reading.

Can You Mix 5w30 and 10w40 Oil

Can I Mix 5w30 and 10w40 Oil?

Yes, you can mix 5w30 and 10w40. However, you must ensure that both of the oils have the same brand. You have to ensure they have the same brands because the additives in oils must be compatible. 

If you mix two motor oils with different brands, they might not mix properly. If you have no choice but to mix them up, then you can do it. You can have your entire oil change after the situation. 

So you can mix the two of these motor oils; if they have different viscosities, you can still mix them both up. The result can be just viscosity, but it is different. The viscosity can be in between the two motor oil that you have mixed.

Can You Add 5w30 to 10w40 Oil?

Yes, you can add 5w30 to 10w40. If you drain the old oil, you are just draining what is in your oil pan; the oil is still left inside your vehicle’s engine. With that, you should know that you are not getting rid of all the oil in your engine. 

So if you switch your oil and choose to go synthetic from conventional, the rest of the old oil will still be inside your engine. With that, the old oil is still mixed up or added up with your new oil. It happens all the time. 

That is why if you top up your current oil with a new one, it is okay. The two of them will not blend, though, but they will still lubricate your engine.

Can You Add 10w40 to 5w30 Oil?

Yes, you can add 10w40 to 5w30 oil. It happens all the time when you will top up your oil. However, the rule of thumb is not to do it. 

You still can if you are left with no choice. For example, if you are left in an emergency, you can add them up.

Related: 5w30 vs. 10w40 Engine Oil

Is It Ok To Mix 5w30 and 10w40 – Possible Downsides?

Yes, you can mix 10w40 to 5w30 if they are on the same brand. The same brands would mean that they are compatible in terms of their additives. However, if you use these motor oil, the new viscosity will be higher than the 5w30 and thinner than the 10w40. 

This means that the viscosity will rebalance and will create a new one. But there are no significant downsides to this. You do not have to worry about major and severe problems. 

The only downside you can have is that your warranty for your vehicle might be voided. So think hard before you start mixing two motor oils.

What Happens if You Mix 5w30 and 10w40 Oil?

If you mix 10w40 to 5w30, it will not improve your vehicle’s performance, and it will also not improve the efficiency of your engine. So the additives will not have any effect at all because of the confusing way they are mixed. 

Therefore, you will not enjoy your motor oil and will not receive all the benefits with the motor oil. Therefore, the rule of thumb is to focus on one motor oil to feel your engine and vehicle benefits.


In summary, people are wondering whether they can mix 10w40 to 5w30. Some people are already doing it. They have not reported any damages to their car; however, there are not many improvements that can happen to your engine. 

Your performance will also not improve. So though the mixing of two motor oil can be done, it is not proven that it can give you benefits and improvements.



Image credits – Canva

Share on:

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