Can I Mix 5w30 And 10w40 Oil? Yes But Not Recommended

We have written several articles about mixing oil types, viscosities (such as mixing 5w20 and 5w30, using 10w30 instead of 5w30, and mixing 5w30 with 5w40), and motor oil brands. As you know, there are many types of multigrade engine oil, and each vehicle requires specific types and viscosity for your engine.

Again, let’s see what you can mix and what you can’t. For instance, can you mix 5w30 and 10w40 if it is the only one available to you then?

mix 5w30 and 10w40

Mixing or topping a 5w30 engine with 10w40 oil is safe and vice versa. However, if you drain the old oil and replace it with the new one, you may experience lower performance. This is because a 10w40 is thicker than a 5w30, so it can put more pressure on the engine and may cause poor fuel mileage and premature wear in some parts.

What is the difference between 5w30 and 10w40?

Now let’s recap the difference between motor oil viscosities and digest the critical difference between 5w30 and 10w40.

5W30 and 10W40 oils are both multigrade motor oils. As mentioned in our previous articles about motor oil, The Society of Automotive Engineers (SAE) assigns a viscosity number, or weight, to oil based on its flow at 210 degrees. The number range indicates the viscosity; the lower the number, the higher, the thicker. W means winter, meaning the number before W is the viscosity in the cold (zero degrees Fahrenheit). The lower the number, the less the oil thickens in cold weather.

The number after the w is the viscosity in hot operating temperature (zero degrees Fahrenheit).

The viscosity of motor oil changes as the temperature goes up or down. For example, if you have a 5W30 oil with an SAE rating of 10W-30 at operating temperature, it will have a consistency of 10 weight at cold temperature. If you have a 5W30 oil with an SAE rating of 15W-30 at operating temperature, it will have a thickness of 15 weight at cold temperature.

So, in a nutshell:

  1. 5w30 and 10w40 have different winter viscosity
  2. 5w30 and 10w40 have different hot or operating temperature viscosity
  3. 10w40 is generally thicker compared to 5w30

Still confused? We found this video from TheRepairSpecialist to help describe the difference between multigrade motor oils:

Can you mix 5w30 with 10w40 oil?

Yes, you can mix 5w30 and 10w40. Your vehicle’s engine will not fall apart if you mix and match different oils, especially if you need a top-up. Mixed engine oil is better than low, dirty, or no oil. However, using thicker oil than recommended will put more stress on the engine resulting in premature wear of engine parts and poor fuel economy.

That is why most experts advise only using the specifically recommended brands for your vehicle. So if it so happens that you accidentally mixed 10w40 with 5w30 as an emergency precaution, drain it and change with the recommended grade as soon as you can.

Here’s why:

The previous section explains that a 10w40 is thicker than 5w30 in cold and hot operating temperatures. If you use thicker oil than recommended, your engine will be under much harsher stress. This is because your engine parts are forced to move through thicker oil.

If you have an older car (before the 21st century), you might not notice a significant difference in fuel economy. However, newer cars have precise engines that require the correct viscosity to run as efficiently as possible. However, newer cars have precise engines that require suitable viscosity to run as efficiently as possible.

Will 10W40 hurt a 5w30 engine?

Since your engine needs to work harder to move the same amount of 10w40 oil around, it can cause premature wear on parts like piston rings and cylinder bores. Also, an oil pump may suffer from using a thicker oil because its purpose is to pump thinner oils around.

So you’re better off using the correct grade of oil for your car from the start rather than trying to convert later down the line. In this case, we highly recommend using 5w30 instead of 10w30 if your engine is designed for 5w30.

If you’re unsure about the grade of oil your car needs, check your owner’s manual. Or ask a mechanic at a local auto repair shop.

Read more: Driving With Bad Oil Pressure Sensor – Why is it Unsafe?


An oil change is one of the most basic yet often overlooked simple car maintenance activities. So should you mix 5w30 and 10w40 oil? Yes, it’s safe to do so in an emergency. But it would help if you only did it when necessary and only when you have a good reason. Mixing two different types of oil, particularly regularly, can cause premature wear and tear on your engine and poor fuel mileage.

This is especially true when you use thicker oil, like 10w40 instead of 5w30. By switching to the correct type of engine oil and then changing it regularly, you can avoid premature wear or damage to your car’s engine.

We hope this article has been helpful to you. If you have any questions or comments, don’t hesitate to leave them below, and we will get back to you as soon as possible.

Elevate your car maintenance game by reading our comprehensive guide on engine oil. Learn everything from the basics of oil types, to how to properly maintain and change it. Keep your vehicle running at its best, read our guide now!

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