- SAE stands for Society of Automotive Engineers, the group that determines standards in motor oils.
- The number that follows SAE is the weight, or viscosity, of the oil. Lower numbers represent thinner oils, and higher numbers are thicker oils.
- Both SAE 30 and SAE 20 motor oils are tested at 100 degrees C (210 degrees F) and will function at their respective viscosity ratings regardless of temperature. This is because they lack additives that keep oil fluid in extremely cold temperatures, which can make cold starts difficult in winter time.
- Oil with this format differs from standard SAE types because it has been tested at both the standard SAE temperatures and at a lower temperature, making it Winter grade (hence the W).
- SAE 30 oil can be used in modern vehicles but commonly is not. Oils containing additives that lower viscosity (make it thinner) at lower temperatures are more commonly used. These are referred to as 5W-30 or 10W-30.
SAE 20 and 30 weight oils are most commonly used in smaller gasoline engines--like those found in lawnmowers--that don't need to be started in cold temperatures.