Can You Mix 5w30 and 5w40 Oil?

Naomi O'Colman

Can You Mix 5w30 and 5w40 Oil?

Can You Mix 5w30 and 5w40 Oil?

Different oil grades are used in different engines. Engines with a higher operating temperature, such as performance engines, typically utilize thicker oils since the oil thins out as the engine temperature rises, and the oil performs better while it is still rather thick as compared to a lower viscosity oil. So, can you mix  5w30 and 5w40 oil?

Yes, you can blend the two oils because they have the same low-temperature viscosity rating of (5) and would flow uniformly to the top ends. The oils, however, will not combine correctly due to the weight differential (30 and 40). This isn’t going to hurt your engine in any case.

What Is the Difference Between 5w30 and 5w40 Motor Oil?

The lesser the viscosity, the worse the performance since the ability to lubricate the components is reduced. The viscosity index measures an oil’s resistance to thinning at higher temperatures.

Engine oil should not be too thick, as it might get too thick at low temperatures, making it difficult to start the engine because the crankshaft is partially submerged in oil.

  Can You Soak Fuel Injectors to Clean Them?

New synthetic oils are made to flow better even at low temperatures because of this. Fully synthetic oils are designed to handle more demanding operating conditions and higher operating temperatures, such as those seen in sports vehicles and pickup trucks that carry hefty loads.

Let’s have a look at the differences between 5w30 and 5w40 engine oils now. The W stands for WINTER, and the digits denote the viscosity of multi-grade oils. Let’s use the 5w30 as an example.

The first number, 5, represents the weight that the oil simulates when it is cold. The last value, 40, represents the oil weight at the engine’s usual operating temperature. In the winter, a 5w30 oil is a 30 weight oil that behaves like a 5 weight oil. In the winter, the 5w40 is a 40 weight oil with a similar weight.

Can You Mix 5w30 and 5w40 Oil?

In most cases, the answer is yes. Different viscosity grades are compatible and mixable, particularly when oil is scarce. It will have no negative impact on your engine.

However, be sure they’re all from the same motor oil manufacturer. Furthermore, mixing the two will result in a new viscosity that is not the same as the manufacturer’s intended viscosity, therefore it’s preferable to switch to the correct viscosity as quickly as possible.

The only practical disadvantage is that none of the oils you blended together will provide your engine with the full benefits it was designed to receive.

Simply said, you can use 5W30 and 5W40 interchangeably; if the engine has been operating with 5W30, increasing to 5W40 won’t affect it, and reducing from 5W40 to 5W30 won’t hurt it either.

  Can ABS Sensor Cause Transmission Problems?

What Happens When 5w30 And 5w40 Oils Are Mixed?

Because the two oils have different weights, they will not combine properly. 5W40 is designed for greater temperatures, but because it is blended with another oil of a different weight, it will not perform to its full capacity in your car engine.

The 5W30 and 5W40 will run evenly into all engine components at low temperatures, which is helpful for fuel economy. In truth, the only thing that occurs when you combine these oils is that the engine will not benefit from the full capacity of both oils.

It’s also worth noting that combining oils might shorten the time between oil changes, requiring you to change or top-up oil more often than before. All of the information in this article applies whether you’re mixing 5W30 and 5W40 from the same brand or from other brands.

However, blending oils from the same manufacturer is preferable because the additives won’t be too dissimilar, and the oils will have a higher chance of mixing well and delivering the greatest possible outcomes.


Can you mix 5W30 and 5W40 oil? Combining different viscosities, such as 5w30 and 5w40, is not a terrible idea, particularly if you are running low on oil, just like mixing full synthetic and semi-synthetic oil. However, if you want to realize the benefits of the motor oil brand’s intentions, this is not the best option. It’s always preferable to be on the safe zone and use what was designed for your automobile in the first place, just like mixing oil brands will change factors that could influence performance.