Can I Mix 5W30 And 10W40 Oil? | Safe Or Not?

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Motor oil is a crucial lubricant in every vehicle, and the right oil ensures the performance and longevity of a vehicle’s engine. There are various viscosity types of motor oils on the market, including 5W30 and 10W40 motor oils. Different viscosity motor oils are designed for different application purposes, and some car owners may wonder if they can mix 5W30 and 10W40 motor oil.

Before we know you can mix 5W30 and 10W40 motor oils, it is better to know the Cranking temperature, pumping temperature, and Cts viscosity. The Cranking temperature is the minimum temperature that oils flow and lubricate engine components in a cold startup. The pumping temperature is the minimum temperature that oil can flow inside the engine and lubricate all the moving parts. Cts viscosity is the motor oil’s ability to maintain viscosity under high shear conditions.

This article will discuss the SAE 5W30 and SAE 10W40 motor oils’ specifications and characteristics, recommended usage, and advantages and disadvantages. And finally, we will explore whether mixing 5W30 and 10W40 motor oil is safe or if there are any potential risks and consequences.

Mix 5W30 And 10W40 Oil

SAE 5W30 Motor Oil Specifications.

The SAE 5W30 motor oil is thinner, its low-temperature viscosity is 5, and its normal operating temperature viscosity is 30. This is a multi-grade oil that consists of SAE 5W and SAE 30.

The SAE 5W cranking temperature is -25°C, the Borderline pumping temperature is -30°C, and the kinematic centistokes (cSt) at 100°C is 3.8. Depending on the additive mixing ratio and package, these temperature ranges may vary slightly in different products. SAE 30 rating kinematic centistokes (cSt) at 100°C between 9.3 to 12.5 (source).


SAE 10W40 Motor Oil Specifications.

The SAE 10W40 motor oil is thicker, its low-temperature viscosity is 10, and its normal operating temperature viscosity is 40. This is multi-grade oil that is a combination of SAE 10W grading and SAE 40. These two gradings have different cranking, pumping temperatures, and kinematic centistokes (cSt).

The SAE 10W has a -25°C Borderline pumping temperature and -20°C cranking temperature, and kinematic centistokes (cSt) at 100°C is 4.1.


Can You Mix 5W30 And 10W40 Oil?

Yes. You can mix 5W30 and 10W40 oils, but it is not recommended. Mixing 5W40 with 10W40 motor oils can change the overall viscosity (depending on the mixing ratio of the two oils). This will result in degrading the lubricant’s performance and reducing the protection, and it can result in increased tear and wear of your engine component.

If you need, you can. However, ensure the two oils have the same base oil and additives before mixing. Generally, the same manufactured oils are safe to mix. However, we recommended using the oil specified in the owner’s manual for best performance and protection.

The 5W30 is thinner, and the 10W40 oil is relatively thicker. So depending on the mixing ratio, your overall oil may be lighter or thicker. Also, using different manufacturers’ different base oils can develop slugs in the long run.


Can You Mix 10W-40 Oil With 5W-30 Oil?

Yes. You can mix 10W40 oil with 5W30 motor oils. However, it is essential to note that 10w40 mixed with 5w30 oils could lower the overall viscosity of the oil, which might pose a problem if you mix more than a quart of 5w30. Suppose the owner’s manual is not recommended 5W30 motor oils. In that case, it can increase engine parts’ wear and tear and reduce the motor oil’s overall performance, especially in high operating temperatures.



Factors To Consider Before Mixing Oils.

Mixing two different SAE grades of motor oils can affect your engine’s performance and protection level. However, mixing the same API grades with different base oils won’t damage the engine, but it reduces the performance. Mixing two different grades of oils can affect oils’ chemical properties like additives, inhibitors, and dispensing and physical properties like viscosity modifiers, pour point depressants, dispersants, and demulsibility agents. Furthermore, it can change cosmetic properties like color.

Therefore, before mixing 5W30 and 10W40 motor oils, ensure the two oils meet the following requirements.

  • Two grades of oil should be the same API grades. (read more about motor oil API certifications here).
  • Two oils should be of the same manufacturer (same brand).
  • Recommendation of the engine manufacturer.
  • Recommendation of the lubricant manufacturer.


Some of the lubricants are not recommended to mix. Because different additive lead to undesirable chemical reactions, which can form deposits. This will lead to expensive repairs.



What happens if I put 10w40 instead of 5w-30?

The SAE 10w40 oil is thicker than 5W30 motor oil. So when you put 10W40, it flows slowly at cold startup, but at high operating temperature, it gradually thins out. Therefore in a cold startup, your engine wear and tear can increase.


What happens if you mix 5w30 and 10w40?

If you mix 5W30 and 10W40 oils, it changes the overall oil viscosity. Furthermore, if the two oils have different additives packages, they can form deposits on the engine components. If you put 5W30 motor oil into 10W40, it reduces the overall motor oil viscosity. On the other hand, if you put 10W40 into 5W30 oil, it increases the oil viscosity. This viscosity change level wholly depends on each oil mixing ratio.

Putting more than a quart of oil can change the quality, performance, and viscosity level, increasing the engine moving parts’ wear and tear in the long run. Before mixing, ensure both oils are in the same API certification. (You can read more about the motor oils API certificate in this post).



Mixing 5W30 and 10W40 oil can change the overall oil viscosity level, quality, and protection. This change wholly depends on the two oils mixing ratio. Putting more than one quart of 5W30 into 10W40 oil changes the overall viscosity of the 10W40. Which means it will become a thinner oil. This might be problematic if the user manual recommended 10W40 or higher SAE-grade oils. Therefore I do not mix different viscosity grade oils.

On the other hand, putting 10W40 into the 5W30 can also be problematic if the user manual recommends 5W30 or lower viscosity level motor oil. Adding a higher SAE grade makes the oil thicker. So it flows slowly at cold startup, and it can increase wear and tear.

Before mixing different SAE-grade motor oils, ensure the two oils are from the same brand and have the same API certification for better results. You can refer to my API grade explanation guide in here.

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