What does the word weight mean in relation to engine oil, like 5 weight oil?
Weight is a scale used by the Society of Automotive Engineers (SAE) to classify viscosity of lubricants. Viscosity is resistance to flow at a given temperature. A low weight, such as five, will flow much faster at a given temperature than a higher weight, such as seventy-five. Temperature must be considered as oil tends to flow more slowly when cold than when hot. Viscosity is often measured in centistokes (cSt) which is roughly, the time it takes a fluid to flow through a given sized orifice at a given temperature, often 40 degrees Celsius. SAE 5 weight oil is roughly equivalent to two centistokes. A more detailed article on oil viscosity is in our Detailed Auto Topics section under Oil Viscosity.
