5W-20 vs 5W-30 vs 10W-30: What's the Difference?

The main difference lies in their viscosity when cold and when the engine reaches operating temperature. Let's first consider 5W-20 versus 5W-30. Then, we'll examine 5W-30 versus 10W-30.

The primary difference between 5W-20 and 5W-30 is their viscosity when the engine reaches operating temperature.

Pay attention to the different numbers in the viscosity rating: "5W" and "20" or "30". The first number (5W) refers to the oil's viscosity when cold, measured at -30°C (-22°F).

5W-20 & 5W-30 versus 10W-30: 5W Oil Flows Faster in Cold Weather

Think of the letter "W" as an abbreviation for "winter." A lower number means the oil will remain more fluid and flow easily through the engine to improve protection during cold starts.

In this case, when comparing 5W-20 or 5W-30 with 10W-30, 5W oil will flow faster in cold weather, as indicated by the lower 5W rating.

This means the oil will flow more easily to lubricate the camshaft lobes, piston rings, cylinders, main bearings, and other critical components during startup. The sooner oil reaches these components, the sooner it protects against wear.

Oil that's too thick can waste valuable seconds with little lubrication reaching engine parts, resulting in wear.

This is especially critical in temperatures below 0°C when oil naturally thickens. Synthetic oil remains more fluid in cold weather to provide better protection than conventional oil. Read this article for more information about the differences between synthetic and conventional oil.

0W-20 versus 5W-20: 0W Oil Flows Better in Cold Weather

The same principle applies when considering 0W-20 motor oil versus 5W-20.

Oil with a lower 0W viscosity rating will remain thinner at cold temperatures and flow slightly faster during cold-weather startups.

The "20" viscosity rating is the same at operating temperature, meaning they will have identical viscosity when the engine has warmed up.

0W oils are becoming more popular because they improve fuel economy through lighter viscosity in cold weather, reducing pump loss.