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

Car drivers have been mixing 5w30 and 5w40 oil. However, many car drivers do not perform the activity because they do not have the possible results. So in this article, let us talk about what happens if you mix 5w30 and 5w40 oil and if you can mix both of them.

So can you mix 5w30 and 5w40 oil? The answer is yes. You can mix a 5w30 oil with a 5w40 oil. However, it is never recommended.

Some car drivers might be confused about the best motor oil for their vehicle – is it the 5w30 or the 5w40. If you are one of these car drivers, you should know this by referring to your owner’s manual. In your owner’s manual, the best and suitable motor oil for your engine will be recommended there. 

Many people have already been mixing 5w30 and 5w40 oil, but most are asking what the result is and the effect that it can cause. A vehicle will need the perfect and suitable motor oil to operate and run properly. Your engine oil will also be the reason for your good or bad performance. 

Good motor oil will improve your fuel economy and will give you that optimum performance. So now, we will talk about whether mixing 5w30 and 5w40 oil will be harmful or not to your engine and what could happen if you mix two of these motor oils. Let us start!

Can You Mix 5w30 and 10w30 Oil

Can I Mix 5w30 and 5w40 Oil?

To answer the question, let us know first the meaning of the names of these oils. Some numbers come before the letter. That number is meant to represent the viscosity of the oil. 

The letter W means winter. The number after the letter is meant to represent the weight of the oil in both high and low temperatures. So to state, the number before the letter W means the viscosity rating, and the number after the letter W means the weight of the oil. 

For both of these oils, the 5w30 and 5w40 oil, it means that both of them will flow evenly in low temperatures. This is because they both have a low viscosity rating, and that is the number five. Both of these oils will weigh differently because they do not have the same weight. 

One of them weighs thirty, and the other weighs forty. So now, you can mix 5w30 and 5w40 oil. They do not pose a dangerous effect. 

The downside is that you might not enjoy the full benefits of one oil because there are other substances from the other oil that you have mixed. So yes, you can mix 5w30 and 5w40 oil.

Can You Add 5w30 to 5w40 Oil?

Yes, you can add 5w30 to a 5w40 oil. However, both of these oils should have the same manufacturer and have the same formulation. 

This is to ensure the maintenance of that additive balance. However, some people have added 5w30 to a 5w40 oil because they have no choice.

Can You Add 5w40 to 5w30 Oil?

Yes, you can also add 5w30 to 5340 oil. Many car drivers have already been doing it. Just do all you can to make sure that both oils have the same brand and make sure that they have the same formulation.

Related: 5w30 vs. 5w40 Engine Oil

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

Yes, it is okay to mix 5w30 and 5w40 oil. The worst situation is an engine failure, and that is pretty unlikely. So the worst scenario that you can have is that you will not enjoy the full benefit of one oil. 

This is because there is another oil that you put in the current oil. So you can mix 5w30 and 5w40 oil. So there will be no dangerous effect that could happen. 

Many car drivers have reported nothing strange or anything bad that happened to their engine. However, if you can avoid the mixing, then you should probably do that. This is because it is not recommended, and no owner’s manual would advise it.

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

If you mix 5w30 and 5w40 oil, the two of them will not mix altogether. They would flow separately. The 5w40 oil is for high temperatures. 

And the full benefits will not be offered to you because there is a mixture of different oil.  For low temperatures, the 5w30 and 5w40 oil will flow just evenly into the components of your engine. So the only upside that you can have is that there is a possibility that the other oil will not unleash its full potential and benefits. 

You will not reap all the good benefits because of the mix itself. So with that, it is essential that you would know the results when you mix 5w30 and 5w40 oil. 

So you need to mix oil with the same brand. This is to ensure that there are no significant gaps and big differences between the two oils.


In summary, mixing 5w30 and 5w40 oil can be done. A lot of car drivers have already been mixing these two oils. Many car drivers are also topping up one oil with a different oil. 

They have reported no changes and no bad results. So you can mix the two of them. The mixture will not cause any severe harm to your engine and its components.



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