What Do the Numbers on Motor Oil Mean?

Last Updated on May 25, 2020

Most people have either changed the oil of their car themselves or they’ve taken their car to a quick lube shop, auto repair shop, or dealership and had professionals do it for them. An important aspect about oil changes involves choosing the right type of oil.

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This doesn’t just mean choosing between synthetic or conventional mineral-based oil. You also need to pay attention to the numbers on the label of the motor oil. You might see something like “10W30” or “5W20” and wonder what the heck they mean.

Even if you have your oil changed by a professional, they normally put a sticker on your windshield which indicates the numbers of the oil they used in your vehicle. What do these numbers mean?

In a nutshell, the numbers before and after the W represent viscosity. The letter “W” itself stands for Winter. As you may know, viscosity means the thickness of a fluid. In the case of motor oil, it is the thickness of the oil under certain temperature conditions.

Related: P0014 Code

The number to the left of the W refers to the oil viscosity when the temperatures are low. The number to the right of the W refers to the oil viscosity at hotter temperatures.

If the first number is low, it means that you have thin oil. Whenever there are colder temperatures in your environment, it is better to have thin oil in your engine. Otherwise, it will be harder for thicker oil to flow throughout your engine and lubricate its components.

The second number will be dependent on two things; the temperature of your engine and the heat of your environment. If you live in a tropical area with a lot of heat, you will want this second number to be high because it means the oil is thick. It is good to have thick oil in hot temperatures because it will do a better job of lubricating the engine’s components.

Read also: 5 Causes of a Car Won’t Go in Reverse

In North America, the standard motor oil to use is 10W30 or 5W30. If you live in a very cold nation like Finland, you might need even thinner oil like 0W30. Likewise, if you live in a very hot country like Nigeria, you could be using 10W40, 20W50, or 15W40.

If you check the owner’s manual of your vehicle, they will tell you the proper viscosity oil grade to use in your vehicle. However, the manufacturer doesn’t always take into account where you are living in the world or where you might be relocating too with your vehicle. Therefore, you need to understand the various types of motor oils so that you can make your own best judgment.



  1. I’ve Always used 5w30 castrol
    Oil in my 1994 cutlass.
    They put in 10w30.
    Will this hurt my engine.
    I’m in a lower climate area also.


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