![]() It was common in areas with large summer to winter temperature variations for an engine to be run on a less viscous oil grade, such as SAE 10, in winter and on a thicker SAE 30 in the summer. This first SAE Viscosity Grades for Engine Oils classification was for ‘straight’ monograde engine oils. In 1911 it established its viscosity grade classifications for engine oils. The Society of Automotive Engineers (SAE) was formed in 1905. ![]() And a multi-grade engine oil has to survive all these different conditions. It provides the appropriate fluid film protection in a number of flow and temperature conditions, being cranked at cold start-up temperatures down as low as -35o C, circulating as the bulk engine oil at around 100o C, or being torn apart through the ring belt area at temperatures around 185o C. Probably the most common multi-grade viscosity classification we encounter is an SAE 15W-40, though some modern diesel engines are now calling for SAE 10W-40, SAE 5W-30 or even SAE 0W-20 viscosity engine oils.Ī multi-grade engine oil is a technological marvel, yet we tend to take them for granted. Any lubricant, including diesel engine oils, can be fully described by those two functions, performance and viscosity. The other is performance, whether an API Service Classification, an ACEA Classification or an OEM specification. Viscosity is one of two characteristics which we use to fully describe an engine oil. We’re all familiar with multi-grade diesel engine oils.
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