What Does an Oil Viscosity Rating Mean?

Oil viscosity ratings, such as 0W-20 or 5W-30, describe how an oil flows at different temperatures. These ratings follow a standard set by the Society of Automotive Engineers and consist of two numbers separated by a “W,” which stands for winter.

Breaking Down the Numbers

The First Number (Cold Temperature Rating)

The number before the “W” indicates how the oil flows in cold temperatures. A lower number means the oil flows more easily when cold, which helps it reach critical engine components faster during startup.

The Second Number (Operating Temperature Rating)

The number after the “W” indicates the oil’s viscosity at normal engine operating temperature. A higher number means the oil maintains a thicker protective film under heat.

0W-20 vs 5W-30 Explained

0W-20 flows extremely easily in cold temperatures and maintains a lighter viscosity at operating temperature, making it common in newer fuel-efficient engines like those in the Toyota Tacoma, Tundra, and many Ford trucks. 5W-30 flows slightly less easily when cold but provides a thicker protective film at operating temperature, making it common in V8 and V6 engines from Ford, Chevy, and Dodge that experience higher loads.

Why Using the Correct Viscosity Matters

Using an oil viscosity outside your manufacturer’s specification can affect fuel economy, cold-start protection, and long-term engine wear. Modern engines are precisely engineered around their specified viscosity grade, including tight tolerances that rely on the oil flowing exactly as designed.

Where to Find Your Vehicle’s Required Viscosity

Check your owner’s manual or the oil filler cap under the hood, which often lists the manufacturer’s recommended viscosity grade directly.

Frequently Asked Questions

Can I use 5W-30 instead of 0W-20 in my truck?

You should always use the viscosity specified by your manufacturer, since deviating can affect fuel economy, cold-start protection, and warranty coverage.

Does viscosity rating affect fuel economy?

Yes, lighter viscosity oils like 0W-20 generally reduce internal engine friction, which can contribute to improved fuel economy compared to thicker oils.

Why do some trucks require thicker oil than others?

Larger displacement engines and those under higher load, such as towing, often benefit from a thicker viscosity at operating temperature to maintain adequate protection.