I've lost track of how many times a customer has picked up...say a bottle of 5W/30 motor oil in my office, looked at the numbers on the bottle and asked me "so this oil is a 5 weight 30"?
Vehicle owners usually know that their car requires a certain viscosity and grade of motor oil as per their owners manual but more often than not don't know what these numbers mean.
The fact is that very few consumers understand today's multi-viscosity motor oil ratings or the nature of how these modern motor oil work as relates to the oils viscosity.
Viscosity is defined as a fluids resistance to flow at a specific temperature.
All multi viscosity motor oils will have two sets of numbers. The top (larger) number indicates the oils viscosity. The most common measurement of oil viscosity is called kinematic viscosity, which measures how fast the oil will flow down through a glass tube heated to 100 degrees centigrade (212F) when pulled through by gravity.