What Is the Importance of Oil Viscosity Classification?

But what exactly is oil viscosity, and why does it matter?

Oil viscosity is the resistance between different layers of oil to slide over one another — in other words, its internal friction. It’s important to note that viscosity is a variable and directly depends on temperature changes.

Therefore, there is a need to classify oils by their viscosity to ensure the right oil is chosen for the engine under specific operating conditions. According to the SAE classification, engine oils are divided into 6 winter grades — 0W, 5W, 10W, 15W, 20W, 25W — and 6 summer grades — 16, 20, 30, 40, 50, and 60. The so-called "Rule of 35" makes it easy to determine the temperature range an oil can handle. For example, by subtracting 5W from 35, we get -30°C, meaning a 5W oil can start the engine in temperatures as low as -30°C.

Before 1993, oils were either for summer or winter use. But thanks to viscosity-modifying additives, multi-grade (all-season) oils are now available.

How Can You Tell Which Viscosity Grade Your Car Needs?

Below are some important points to consider when choosing oil:

Follow the vehicle’s owner’s manual, which specifies the recommended viscosity grades for your car model.

Consider the climate of the region where the car will mostly be used.

Pay attention to the vehicle’s mileage — cars with higher mileage often benefit from slightly thicker oils that better protect a somewhat worn engine.

Remember: Choosing the right viscosity oil not only protects the engine from wear but also helps save fuel, ensures smooth operation, and extends the life of your vehicle.