What Do the Numbers on Oil Mean? (Simple Explanation)

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 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: Symptoms of Using the Wrong Engine Oil 

Oil Viscosity

engine oil typesengine oil types

The 1st Number

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 2nd Number

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.

In the US, two common motor oils in use are 10W30 or 10W40. If you live in an area that has very cold winters like Michigan or pretty much all of Canada, you might need even thinner oil like 0W30. Likewise, if you live in a very hot climate like Arizona, 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.

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