San Diego Gas and Car Wash

What do the viscosity ratings mean?

When we manufacture a multi-grade oil, like a 5W-30, viscosity modifiers (additives) are added to the oil that help the oil to resist it’s natural tendencies to thin and thicken at high and low temperatures.

For example, oil naturally gets thicker at low temperatures, so the viscosity modifiers added to the oil cause the oil to thin out more than it normally would at low temperatures. (like adding water to molasses)

For high temperatures oil wants to thin, so different viscosity modifiers that are put in the oil cause the oil thicken when the oil gets hot (like putting cornstarch in gravy)

Therefore, the oil is able to be thinner at low temperatures (5W) and thicker at high temperatures (30W) than normally possible.

Posted in: Castrol