Can You Mix 5w30 And 5w40 Oil?

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Between 5w30 and 5w40 oil, which is best for your engine? First of all, which of these oils was indicated in your car’s manual – whichever one in your manual is the best for your engine.

However, many drivers do mix engine oils for several reasons. But can you mix 5w30 and 5w40 oil?

Apparently, a car cannot function properly if the engine lacks sufficient oil. Also, the type of oil you use for your car engine will determine its performance and duration.

Typically, motor oils are formulated to enhance car engine performance and improve fuel efficiency; however, when mixed, this purpose is somehow dented.

Can You Mix 5w30 And 5w40 Oil?

Let’s explain the difference between these two oils – it’d make you understand our conclusion/answer to the question. The numbers you see on different oils (before and after the letter “W” – the “W” represents “Winter”) represent the viscosity and weight of the oil in low and high temperatures.

The number before the letter is the viscosity rating, while the number after the letter is the weight.

For 5W30 and 5W40, it implies that both oils will flow evenly at low temperatures because they both have a low viscosity rating of “5.” On the other hand, both won’t be the same in high temperatures because they have different weights, “30” and “40,” respectively.

Now that you’ve known the differences, let’s see what happens when you mix both oils. But then, generally, it is not bad to mix two oils of different weight or viscosity.

The only practical CON is that your engine won’t get the full benefits it was supposed to get from either of the oils you mixed together.

Simply put, you can mix 5W30 and 5W40; if your engine has been running with 5W30, upgrading to 5W40 won’t be any worse, and downgrading from 5W40 to 5W30 won’t hurt your engine either.

What Happens When You Mix 5w30 And 5w40 Oil?

Can You Mix 5w30 And 5w40 Oil

Since the oils have different weights, they won’t properly mix together. Basically, 5W40 is meant for higher temperatures, but it won’t deliver its full potential to your car engine because it is mixed with another oil of different weight.

Both 5W30 and 5W40 will flow evenly at low temp into all the engine components – this viscosity rating is good for fuel economy. In fact, the only thing that happens when you mix these oils is that your engine won’t enjoy the full potentials of both oils that have been mixed together.

It is also important to know that mixing oils can reduce the gap between oil changes; you may now have to change/top-up oil more frequently than before. Whether you’re mixing 5W30 and 5W40 from the same brand or different brands, all that has been shared in this article still applies.

But it’d be best to mix oils from the same brand – the additives won’t be too different, so the oils will have better chances of mixing properly to deliver the best possible results.


So, can you mix 5W30 and 5W40 oil? Yes, you can mix both oils – they have the same low temp viscosity (5) rating and would flow evenly to the top ends. However, because of the difference in weight (30 and 40), the oils won’t mix properly. This doesn’t pose any harm to your engine anyway.

Furthermore, you can mix synthetic oils with semi-synthetics or even high-mileage oils. Mixing different oils won’t hurt your engine but won’t improve the performance either. We’d advise that you keep up with the recommended oil for your car engine, as indicated in the manual.

Since oil blends or mixed oils don’t promise any good advantages, there’s apparently no need to practice such acts. You could even end up voiding your car’s warranty coverage.

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