Viscosity of motor oil (Audi 80 B3)

Depending on the temperature, the viscosity of the oil changes. As the temperature increases, it becomes more liquid. The strength of the oil film deteriorates. The extrusion resistance decreases. When cold, the oil is dense and viscous, the fluidity is poor and internal friction increases. When operating, a motor oil is required that would change as little as possible with temperature changes.

When the engine is cold, it should be fluid enough not to overly hinder the starter's operation. And after starting, it should flow to the lubrication points as quickly as possible.

Viscosity is the internal friction of the oil, which is designated by the SAE system (Society of Automotive Angineers), such as SAE-30, SAE-10, etc. A higher SAE number indicates a thick oil, a lower one indicates a thin oil. But viscosity cannot be used to judge the lubricating properties of oil.