Base Stock: The base fluid, usually a refined petroleum fraction or a selected synthetic material, into which additives are blended to produce finished lubricants.
Blow-by: Passage of combustion gases past the piston rings causing contamination of the crankcase oil.
Brookfield Viscosity: Viscosity at a controlled temperature and shear rate.
Centipoise: Unit of measure for the viscosity of a fluid. One centipoise equals 0.01 Poise and is equivalent to one milliPascal-sec (mPa-s) in SI units.
CentiStoke: Unit of measure for the kinematic viscosity of a fluid. One centistoke equals 0.01 Stokes and is equivalent to one mmª/sec in SI units.
Cold Cranking Simulator (CCS): An intermediate shear rate viscometer that determines the ability of an oil to allow a satisfactory cranking speed in a cold engine.
Density: Mass per unit volume.
Exhaust Gas Recirculation (EGR): An engine system designed to lower the emission of nitrogen oxides (NOx). It routes exhaust gases into the carburetor or intake manifold and reduces peak combustion temperatures, thereby reducing the tendency for NOx to form.
Kinematic Viscosity: Fluid's resistance to flow under gravity at a specific temperature (usually 40°C or 100°C).
Lubrication: Creation of a friction-reducing film between moving surfaces that are in contact, reducing wear.
Multigrade Oil: Engine or gear oil that meets the requirements of more than one SAE viscosity grade classification, and that can be used over a wider temperature range than a single grade oil.
Poise (P): Unit of measure for the viscosity of a fluid, or its resistance to flow, defined by the shear stress (in dynes per square centimeter) required to move one layer of fluid along another over a total layer thickness of one centimeter at a velocity of one centimeter per second. This viscosity is independent of fluid density, and directly related to flow resistance.
Shear Stability Index (SSI): A measure of an oil's irreversible viscosity loss attributable to the viscosity index improver when the oil is subjected to engine operation or special test conditions.
Stoke (St): A unit of measure of kinematic viscosity defined by the ratio of the fluid's dynamic viscosity to its density. Usually expressed as centistokes (CST), where 1 Stoke = 100 CST and 1 CST = 1 mmª/s.
Viscosity: A measure of a fluid's resistance to flow.
Viscosity Index (VI): Relationship of viscosity to the temperature of a fluid. It is determined by measuring the kinematic viscosities of the oil at 40 and 100°C and using the tables or formulas included in ASTM D 2270. High viscosity index fluids tend to display less change in viscosity with temperature than low viscosity index fluids.
Viscosity Index Improver (VII): Lubricant additive, usually a polymer, that provides beneficial rheological properties to lubricating oils, such as reducing the tendency of viscosity to change with temperature.
