Motor oil gets thinner as it's heated, but to prevent it from getting too thin at higher temperatures, additives (viscosity modifiers) are used so that it behaves like a thicker grade oil at higher temps.

Does oil get thicker as it warms up?

Oil weight, or viscosity, refers to how thick or thin the oil is. ... Your engine needs oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils.

Does motor oil get thicker or thinner when hot?

Motor oil includes additives developed to reduce changes in viscosity because of temperature. Certain motor oils are designed to be thinner (less viscous) when cold and more viscous (thicker) when hot.