Physical and Chemical Properties of Engine Oils
|Publication Date:||1 May 1984|
Introduction- This SAE Information Report discusses a number of the physical and chemical properties of new and used engine oils. Where appropriate, standardized methods of test for these properties are listed. This report was prepared to provide those concerned with the design and maintenance of internal combustion engines with information relative to the terms used to describe engine lubricants.
In addition to the basic function of lubrication (reducing friction and wear between moving parts), the oil must also (1) provide a seal between cylinder walls, pistons, and piston rings, (2) dissipate heat from critical areas, (3) neutralize acids formed during combustion, (4) disperse contaminants to prevent accumulation of deposits, (5) protect internal engine parts from rust and corrosion, and (6) control oxidation to prevent excessive viscosity changes. In performing these functions, the oil can be subjected to extreme temperature variations, ranging from below -40°C during shutdown periods in winter to 200°C or higher while the engine is operating. In certain engine configurations, such as turbocharged, hot soak temperatures after shutdown can exceed 350°C in areas where engine oil is present. A wide variety of contaminants may be introduced into the crankcase by way of blow by or fresh-air ventilation. While some contaminants are inert, others are chemically active or can catalyze chemical reactions, some of which may be undesirable.