Motor oil is one of the most basic car maintenance items. Designed to prevent the moving parts of an engine from stiffening by lubricating them as needed, motor oil must be just as reliable at freezing temperatures as in the extreme heat of a running engine. Aside from reducing friction, motor oil also cools and insulates components the cooler fluid can't reach. There are several types of motor oils: mineral motor oils, made from petroleum distillates, synthetic motor oils, and semi-synthetic motor oils, which are a mixture of both synthetic and mineral base oils. Oils designed for two-stroke engines shouldn't be used in four-stroke engines, but synthetic and mineral oils can be mixed as long as they have the same performance grade.
Motor oil designations
One question is unavoidable when buying motor oil: all those names and numbers - Castrol, Mobil, 5W-40, 0W-40 - what do they mean? The brand name can have an impact, but what is most important when looking for motor oil is the viscosity. Most of the time it's enough to take a look at the manufacturer's recommendations to find the SAE viscosity class, as well as any API classification and ACEA specification needed for a car. These should generally be respected, among other reasons because not doing so can void the warranty of a car. Viscosity refers to the internal friction of a fluid. SAE stands for Society of Automotive Engineers and signifies the grade of a motor oil, while differentiating between summer and winter oils (also known as single grade oils). Most drivers prefer multi-grade oils, which are suitable for all seasons - for example, a SAE 10W-40 oil. The number in front of the “W” (which is short for 'winter', meaning that the oil can be used in winter) stands for the motor oil's minimum viscosity. The number behind the “W” indicates the maximum temperature at which the oil can be pumped.