Updated at: 19-03-2022 - By: micdot

This article contains affiliate links. There is no additional cost to you, and I may receive a small compensation if you make a purchase after clicking on one of my links. What’s the difference between 5w30 and 5w40 oil? First of all, check your car’s owner’s manual to see which of these oils is recommended for your vehicle’s engine. However, for a variety of reasons, many motorists mix their engine oils. However, can you use 5w30 and 5w40 oil in the same vehicle?

It appears that a car’s engine will not run correctly if there is not enough oil in it. Your car engine’s performance and lifespan are also influenced by the type of oil you use. However, when blended with other types of motor oil, their intended function is reduced in some way.

Can You Mix 5w30 And 5w40 Oil?

To help you grasp our answer, we’ll go over the differences between these two oils. Temperature-dependent viscosity and weight are represented by the numbers you see on different oils (before and after the letter “W”—the “W” signifies “Winter”). The viscosity rating appears before the letter, while the weight rating appears after the letter.

5W30 and 5W40 both have a viscosity rating of “5”, which indicates that they will flow evenly at low temperatures. However, because they have different weights, “30” and “40,” they won’t be the same in high temperatures. Once you’ve established the distinctions between the oils, it’s time to see what occurs when you combine them. However, in general, it is not a terrible idea to combine two different types of oil. There is only one practical drawback: Your engine won’t get the full benefits of either of the oils you put together.

So long as your engine has been running on 5W30, increasing to 5W40 won’t hurt it, and reducing back to 5W30 won’t harm it either.

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

Because the weights of the oils are different, they will not be able to combine correctly. Because it is blended with another oil of a different weight, 5W40 isn’t able to perform to its full potential in your car’s engine because it was designed for higher temperatures in the first place. The viscosity grade of 5W30 and 5W40 ensures that oil flows uniformly throughout the engine’s components even at low temperatures, which helps to improve fuel economy. However, the engine won’t be able to take advantage of the full potentials of both oils because they have been mixed together.

When it comes to oil changes, it is crucial to keep in mind that mixing oils can shorten the interval between them. You can use the information in this article whether you’re blending 5W30 and 5W40 from a single brand or from multiple manufacturers. To get the greatest results, it’s advisable to use oils from a single brand because the additives won’t be so different, thus the oils will be more likely to mix effectively.


Can 5W30 and 5W40 motor oils be combined? Both oils have the same low-temperature viscosity rating of (5) and would flow equally to the ends if mixed together. As a result, the oils will not mix correctly due of their differing weights (30 and 40). Your engine won’t be affected by this at all.

It’s also possible to combine synthetic oils with semi-synthetic or even high-mileage oils. The engine won’t be harmed by mixing different oils, but it won’t get any better either. We recommend that you follow the instructions in your car’s owner’s manual and use the proper oil for your vehicle’s engine. There appears to be no reason to engage in the practice of oil blends or mixed oils, given that no benefits have been demonstrated. It’s possible that you’ll void your car’s warranty.