Synthetic Oils

Compared with conventional motor oils, the synthetics involve different chemical processes and ingredient percentages. However, the base stock still comes from crude petroleum, and the additives are virtually the same as those commonly used.
From a performance standpoint, they work well, especially for engine start-up at very low temperatures. But, based on all the information, synthetic oils can not be left in an engine any longer than conventional oils (extended use is the principal claim of synthetics). They can be used, but must have the right service category, viscosity grade and fuel efficiency designation for the vehicle. The oil must be changed as specified in your owner's manual.
A second category (beginning with the letter "C") also exists. These oils (CC, CD, CE, etc..) are intended for diesels, like in trucks and bulldozers, and by themselves are not suitable for gasoline engines.