SAE Viscosity Grade
The most widely used system for rating the viscosity of oils was established
by the SAE (Society of Automotive Engineers) in the USA. Simply put, this is
the measure of an oil’s ability to flow to critical lubrication sites
in the engine at certain temperatures and to lubricate when there. An oil's
viscosity rating is often referred to as its 'grade'. There are two types of
viscosity grades -- those containing the letter W (for Winter) and those without
the W.
Multigrade oils, such as SAE 10W30 oil, satisfy the viscosity requirements of one of the W grades at low temperature and one of the non-W grades at high temperature. Multigrade oils are widely used because they are formulated to allow the engine to start when the engine is cold but also to maintain sufficient viscosity to protect the engine at higher temperatures and operating loads. The number before the W represents its viscosity rating when cold. The number after the W represents it viscosity rating closer to operating temperatures.
We recommend following the engine manufacturer's suggestions for viscosity grade when choosing an oil for normal driving conditions.
Click Viscosity for more information on the most important property of your engine oil.