ACRONYMS

ACEA - Association of European Automotive Manufacturers
AGMA - American Gear Manufacturers Association
API - American Petroleum Institute
ASLE - American Society of Lubrication Engineers
ASME - American Society of Mechanical Engineers
ASTM - American Society for Testing and Materials

BPT - Borderline Pumping Temperature
BTU - British Thermal Unit

CARB - California Air Resources Board
CCS - Cold Crank Simulator
CEC - Conseil Europen de Coordination pour les
CMA - Chemical Manufacturers Association
cP - CentiPoise
cSt - CentiStoke
COC - Cleveland Open Cup

DIN - Deutsche Industrie Norm

EGR - Exhaust Gas Recirculation
EHD or EHL - Elastohydrodynamic Lubrication
EMA - Engine Manufacturers Association
EP - Extreme Pressure

ILSAC - International Lubricant Standardization and Approval Committee
ISO - International Organization for Standardization

JAMA - Japanese Automobile Manufacturers Association Inc.
JASO - Japan Automobile Standards Organization

MSDS - Material Safety Data Sheet

NLGI - National Lubricating Grease Institute
NMMA - National Marine Manufacturers Association

PAO - Polyalphaolefin

SAE - Society of Automotive Engineers
STLE - Society of Tribologists and Lubrication Engineers
SUS or SSU - Saybolt Universal Seconds

TAN - Total Acid Number
TBN - Total Base Number

VI - Viscosity Index
VII - Viscosity Index Improve

ZDP - Zinc Dithiophosphate

 

COMMON TERMS

Abrasion - The wearing, grinding, or rubbing away by friction. Abrasion is usually due to the presence of foreign matter such as dirt, grit or metallic particles in the lubricant 

Absolute Viscosity - The product of Kinematic Viscosity and Density.
Absolute Viscosity (n) = Kinematic Viscosity (y) x Density (p).

Acid - Corrosive solution formed by the combination of hydrogen and oxygen atoms with metal or metallic radicals. Acidic solutions may be neutralized with a base or alkaline solution. 

Acid Number - A measure of the amount of KOH needed to neutralize all or part of the acidity of a lubricant

Additive - Material added to a base stock to change its properties, characteristics or performance.

Adhesion - The property of a lubricant that causes it to cling or adhere to a solid surface. Wear occurring when surfaces contact, weld together and shear off.

Air Entrainment - The incorporation of air in the form of bubbles dispersed in a fluid. Common when an improper amount of antifoam agent is added to reduce foaming.

Ambient Temperature - Temperature of the air surrounding the point of application.

Anhydrous - Free of water. 

Antifoam - Additive used to suppress the foaming tendency of lubricants in service. Improper amounts of antifoam will lead to air entrainment, which also leads to lubrication problems.

Antifreeze - Solution in an engine cooling system that lowers the coolants freezing point and raises its boiling point.

Antioxidant (oxidation inhibitor) - An additive that retards oxidation of lubricants.

Antiwear - Additives that form thin tenacious films on loaded parts to prevent metal-to-metal contact.

Apparent Viscosity - A measure of the viscosity of a non-Newtonian fluid under specified temperature & shear. Viscosity is expressed in units of centipoise (cP). 

Ash - Metallic deposits formed in the combustion chamber and other engine parts during high temperature operation.

Ash (Sulfated) - The ash content of an oil, determined by charring the oil, treating the residue with sulfuric acid, and evaporating to dryness. Expressed as % per mass.

Ball Bearing - A class of bearing in which the moving surface is separated from the stationary surface by elements in the form of balls.

Bases - Compounds that react with acids to form salts plus water. Alkalis are water-soluble bases used in petroleum refining to remove acidic impurities. Oil soluble bases are included in lubricating oil additives to neutralize acids formed during the combustion of fuel or oxidation of the lubricant. 

Base Stock - The base fluid, usually a refined petroleum fraction or a selected synthetic material, into which additives are blended to produce finished lubricants.

Base Number - The amount of acid needed to neutralize all or part of a lubricants basicity.

Bearing - An object that supports weight and reduces friction by allowing a surface to rotate or slide when under load.

Biodegradable - Ability of a material can be broken down, within given parameters of time and environment, by naturally occurring bacteria into simple substances, which do not harm the environment.

Bleeding - Separation of liquid lubricant from a grease.

Blow-by - Passage of unburned fuel and combustion gases past the piston rings of internal combustion engines, resulting in fuel dilution and contamination of the crankcase oil.

Boundary Lubrication - Lubrication between two rubbing surfaces without the development of a full fluid lubricating film. It occurs under high loads and requires the use of antiwear or extreme-pressure additives to prevent metal-to metal contact.

Brinelling - Denting caused by impact of one bearing component against another while stationary.

By-Pass Filtration - A system of filtration in which only a portion of the total flow of a circulating fluid system passes through a filter at any instant or in which a filter having its own circulating pump operates in parallel to the main flow.

Carbon Residue - Coked material remaining after an oil has been subjected to high temperatures.

Cavitation - The formation and collapse of vapor bubbles within a liquid.

Centipoise (cP) - Unit of measure for apparent viscosity. 

Centistoke (cSt) - Unit of measure for Kinematic Viscosity.

Cetane Index - A value calculated from the physical properties of a diesel fuel to predict its Cetane Number.

Cetane Number - Measure of ignition quality of a diesel fuel. The higher the Cetane Number, the easier a high-speed, direct injection engine will start, and the less white smoking and diesel knock after start up. 

Cetane Number Improver - An additive that boosts the Cetane Number of a fuel while improving combustion efficiency and increasing power in a diesel engine.

Channel Point - See pour point. As you reduce the temperature of an oil toward the pour point, you reach a point where you can run your finger through an oil and it will not fill in the trench you leave behind. Example: the gearing in the rear end of a car. Although the gears might move, the gear oil will not flow back into the gear to lubricate it readily.

Chemical Stability - The tendency of a substance or mixture to resist chemical change. 

Cleveland Open Cup (C.O.C.) - An apparatus used to determine the flash and fire points of petroleum products other than fuel oils and those having an open cup flash below 79C/175F.

Cloud Point - The temperature at which a cloud of wax crystals appears when a lubricant or distillate fuel is cooled under standard conditions. Indicates the tendency of the material to plug filters or small orifices under cold weather conditions.

Coefficient of Friction - Number obtained by dividing the frictional force resisting motion between two bodies (F) by the normal force pressing the bodies together (L). m = F L

Cohesion - That property of a substance that causes it to resist being pulled apart by mechanical means.

Cold Cranking Simulator (C.C.S.) - An intermediate shear rate viscometer that predicts the ability of an oil to permit a satisfactory cranking speed to be developed in a cold engine.

Combustion Chamber - The space between the piston and cylinder head in an internal combustion engine where the charge of fuel plus air is burned to produce power.

Compatibility - A lubricants ability to be mixed with another lubricant without detriment to either lubricant. Also, the ability to come into contact with other components or materials without detrimental effects.

Compound - Substance formed by the combination of two or more elements with differing physical and chemical properties than the combining elements.

Compression Ignition - Ignition of fuel by the heat generated in compressing the air charge, as in the diesel engine.

Compression Ratio - The ratio of the volume of combustion space at the bottom dead center to that at top dead center, in an internal combustion engine.

Consistency - The degree to which a semi-solid material such as grease resists deformation.

Contaminant - Any material that is unwanted or adversely affects the fluid power system and/or its components.

Coolant - Fluid used to remove heat. Commonly found in an engines cooling system. 

Copper Strip Corrosion - Qualitative measure of the tendency of a liquid to corrode pure copper.

Corrosion - Destruction of a metal by chemical or electo-chemical reaction with its environment.

Corrosion Inhibitor - Additive that protects lubricated metal surfaces from chemical attack by water or other contaminates.

Cracking - Refining process in which large molecules are broken down into smaller molecules. Cracking takes place to some extent whenever high molecular material is heated strongly, but can be increased by catalysts.

Crankcase - The housing in which the crankshaft and many other parts of the engine operate. On a two-cycle engine, the area in which the fuel/oil mixture is drawn before being transferred to the cylinder.

Crankcase Dilution - When unburned fuel finds its way past the piston rings into the crankcase oil, where it dilutes or thins out the engine lubricating oil.

Crude Oil - Naturally occurring petroleum, before any refining or treatment.

Demulsibility - The measure of a fluids ability to separate from water.

Density - Mass per unit of volume.

Detergent - Additive to keep engine parts clean. In motor oil formulations, the most commonly used detergents are metallic soaps with a reserve of basicity to neutralize acids formed during combustion.

Detonation - Uncontrolled burning of the last portion (end gas) of the air/fuel mixture in the cylinder of a spark-ignition engine. Also known as knock or ping.

Differential - Set of gears that transfers the power from the drive shaft to the drive wheels and allows those wheels to turn at different speeds. 

Dispersant - Additive that helps keep solid contaminants in crankcase oil in colloidal suspension, preventing sludge and varnish deposits on engine parts. Usually nonmetallic (ashless), and used in conjunction with detergents.

Distillation - Separation of a mixture of liquids with different boiling points by progressively raising the temperature. In a refinery distillation unit the temperature rises continuously from the top to the bottom of the column and different fractions or cuts are drawn off at different heights.

Distillation Test - The basic test used to characterize the volatility of a gasoline or distillate fuel.

Drag - Resistance to movement caused by oil viscosity.

Dropping Point - Temperature at which a grease passes from a semi-solid to a liquid state under specified test conditions.

Drum - A cylindrical container that holds 55 gallons of oil or approximately 400 pounds of grease type products. There are also half-size drums that hold approximately 30 gallons of oil.

Dynamic Viscosity - Viscosity of a liquid as measured in a rotational instrument, as distinct from the kinematic viscosity where the liquid falls through a capillary tube under its own weight.

E.G.R. (Exhaust Gas Recirculation) Valve - System to reduce automotive emission of nitrogen oxides (Nox). It routes exhaust gases into the intake manifold where they dilute the air/fuel mixture and reduce peak combustion temperatures, thereby reducing the tendency for Nox to form.

Elastohydrodynamic Lubrication (EHD or EHL) - Lubrication characterized by high unit loads and high speeds in rolling elements where the mating parts deform elastically due to the incompressibility of the lubricant film under very high pressure.

Elastomer - A rubbery type of material. 

Emissions - Term used generically to refer to the various components of the engines exhaust.

Emulsifier - Substance used to promote or aid the formation of a stable mixture, or emulsion of oil & water.

Emulsion - Mixture of two liquids, which are not soluble with each other, such as oil and water. 

Engine Deposits - Hard or persistent accumulation of sludge, varnish and carbonaceous residues due to blow-by of unburned and partially burned fuel, or the partial breakdown of the crankcase lubricant. Water from the condensation of combustion products, glycol, carbon, residues from fuel or lubricating oil additives, dust and metal particles also contribute.

EP (Extreme Pressure) - Lubrication regime where surfaces are sliding against each other under heavy load. The expression was coined for the condition present in hypoid gears in automotive rear axles.

EP (Extreme Pressure) Lubricants - Lubricants that impart to rubbing surfaces the ability of carrying greater loads than would be possible with ordinary lubricants without excessive wear or damage.

Erosion - The wearing away of a surface by an impinging fluid or solid

Ester - An organic compound formed by the reaction of an acid (organic or inorganic) with an alcohol. 

Ethanol - Ethyl alcohol mainly formed through fermentation. (alcoholic drinks, component in gasohol)

Ethylene Glycol - A colorless, syrupy liquid, used as an antifreeze in cooling and heating systems.

Evaporation Loss - The loss of a portion of a lubricant due to volatization.

Fillers - A term normally used to denote something non-chemical added to an oil or grease, i.e., moly, graphite, zinc oxide.

Film Strength - The ability of a lubricant film to withstand the effects of speed, temperature and load without breaking down.

Filter - Any device or porous substance used for cleaning and removing suspended matter from a gas or fluid.

Fire Point - The temperature where a lubricant, when subjected to a source of ignition or flame, ignites & continues to burn.

Fire Resistant Fluid - A fluid, difficult to ignite, that shows little tendency to propagate flame.

Flash Point (C.O.C.) - The temperature to which a combustible liquid must be heated to give off substantial vapor to form a momentarily flammable mixture with air when a small flame is applied under specific conditions.

Fluid - Liquid, gas or combination thereof.

Fluid Friction - Occurs between the molecules of a gas or liquid in motion, and is expressed as shear stress. Unlike solid friction, fluid friction varies with speed and area.

Fluid Power - Energy transmitted and controlled through use of a pressurized fluid within an enclosed circuit.

Foam - An agglomeration of gas bubbles separated from each other by a thin liquid film. If an oil is said to not foam, the small air bubbles will quickly combine, become larger bubbles, and then break to vent to the atmosphere. If this action occurs slowly, the oil is said to foam.

Four Ball Test - Machine used to evaluate a lubricants antiwear qualities, frictional characteristics, or load carrying capabilities. There are four steel -inch balls. Three of the balls are clamped together in a cup filled with lubricant while the fourth ball is rotated against them. Two test procedures are based on this same principle the Four Ball EP Test (ASTM D-2596) and Four Ball Wear Test (ASTM D-2266). 

Four Stroke Engine - An internal combustion engine that requires two revolutions of the crankshaft to complete all four cycles.

Fretting - Wear resulting from small amplitude motion between two surfaces; may produce red or black oxide.

Friction - Resistance to motion of one object over another. Friction depends on the smoothness of the contacting surfaces, as well as the force with which they are pressed together.

Fuel Dilution - The amount of unburned fuel present in the lubricant. This test will indicate problems such as fuel line, injector, carburetor and pump leaks. Fuel dilution is accurate down to less than 0.5%.

Full Film Lubrication - Complete separation of mated surfaces. No metal-to-metal contact.

Full-Flow Filtration - A system of filtration in which the total flow of a circulating fluid system passes through a filter prior to component delivery.

Gears - Toothed machine parts for transmitting power from one shaft to another.

Gravity - The mass/volume relationship of lubricants used in determining volume requirements for specific mass of products (packaging).

Grease - Lubricant composed of an oil or oils thickened with a soap, soaps or other thickener to a semi-solid consistency.

Gum - A rubber like, sticky deposit black or dark brown in color resulting from the oxidation of lubricating oils from unstable constituents in gasoline, which deposit during storage or use.

High Temperature High Shear Rate Viscosity (HTHS) - A measure of a fluids resistance to flow under conditions resembling highly-loaded journal bearings in fired internal combustion engines, typically 1 million s-1 at 150oC.

Horsepower - A measurement of an engines power, equal to 550 foot pounds of torque per second.

Hydrocarbons - Compounds of hydrogen & carbon of which petroleum products are typical examples. Also known as organic compounds.

Hydrodynamic Lubrication - The formation of a continuous lubricating fluid film between mating surfaces of sufficient pressure to prevent contact

Hydro finishing - A process for treating raw extracted base stocks with hydrogen to saturate them for improved stability.

Hydrolytic Stability - Ability of additives and certain synthetic lubricants to resist chemical decomposition (hydrolysis) in the presence of water.

Hypoid Gear Lubricant - A gear lubricant having extreme pressure characteristics for use in hypoid type gears (as in the differential of an automobile).

Incompatibility - When a mixture of two or more substances shows physical properties or service performance characteristics, which are inherently inferior to those of either of the individual products before mixing.

Inhibitor - Additive that improves the performance of a petroleum product by controlling undesirable chemical reactions, i.e., oxidation inhibitor, rust inhibitor, etc.

Insolubles - Contaminates found in used oils due to dust, dirt, wear particles or oxidation products. 

Journal - Part of shaft or axle that rotates or angularly oscillates in or against a bearing or about which a bearing rotates or angularly oscillates.

Keg - Container which would typically hold 16 gallons of oil or approximately 120 pounds of a grease-type product. Also called a quarter drum.

Kinematic Viscosity - Measure of a fluids resistance to flow under gravity at a specific temperature (usually 40C or 100C).

Lubrication - Control of friction and wear by the introduction of a friction reducing film between moving surfaces in contact. May be a fluid, solid or plastic substance. 

Material Safety Data Sheet (MSDS) - Vital information regarding the safe handling and storage of a product.

Micron - A millionth of a meter, or 0.0000394 inch.

Mineral Oil - Term applied to a wide range of products that is typically used when referring to petroleum-based lubricants.

Mini Rotary Viscometer - An instrument used to measure the borderline pumping temperature (BPT) of engine oils from 0C to -40C. BPT is the lowest temperature at which engine oil can be supplied in adequate amounts to the oil pump inlet.

Multi-viscosity/Multi Grade 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.

Naphthenic - A type of petroleum fluid derived from naphthenic crude oil, containing a high proportion of closed-ring methylene groups.

Neutralization Number - A measure of the acidity or alkalinity of an oil.

Newtonian Flow - Occurs in a liquid system where the rate of shear is directly proportional to the shearing force, as with straight grade oils which do not contain polymeric viscosity modifier. When rate of shear is not directly proportional to the shearing force, flow is non-Newtonian, as it is with oils containing viscosity modifiers.

Nitration - Process where nitrogen oxides attack petroleum fluids at high temperatures, often resulting in viscosity increase and deposit formation. Nitration only occurs in applications where fuel is used.

NLGI - National Lubricating Grease Institute, an industry group that monitors grease and sets penetration standards for grading greases.

NLGI Number - A scale for comparing the consistency (hardness) range of greases.

Octane Number - A measure of a fuels ability to prevent detonation in a spark-ignition engine. 

Organic Acid - An organic compound, with acid properties, obtained from organic substances such as animal, vegetable and mineral oils, i.e., a fatty acid.

Oxidation - Occurs when oxygen attacks fluids. The process is accelerated by heat, light, metal catalysts and the presence of water, acids, or solid contaminants. It leads to increased viscosity and deposit formation.

Oxidation Inhibitor - Substance added in small quantities to an oil product to increase its oxidation resistance, thereby lengthening its service or storage life. Also called an antioxidant.

Oxidation Stability - Resistance of an oil product to oxidation and, therefore, a measure of its potential service or storage life.

Oxygenated Fuels - Fuels for internal combustion engines that contain oxygen combined in the molecule, e.g., alcohols, ethers and esters. Term also applies to blends of gasoline with oxygenates, e.g., Gasohol, which contains 10% by volume of anhydrous ethanol in unleaded gasoline.

Paraffin - Hydrocarbons belonging to the series starting with methane (CH4). Paraffins are saturated with respect to hydrogen. High molecular weight paraffins are solid such as paraffin wax.

Particle - A minute piece of matter with observable length, width and thickness, usually measured in micrometers.

PCV (Positive Crankcase Ventilation) Valve - An emissions control device that allows gases from the crankcase to be reintroduced into the intake.

Penetration - A test in which a cone is dropped into a grease sample to measure the penetration or how hard or soft the grease is at room temperatures. The cone penetrates farther in a soft grease and therefore has a higher penetration number. This penetration relates to an NLGI number. A number 0 grease is called an NLGI 0 grade and will be softer than an NLGI 1 or 2 grade.

pH - A measure of acidity or alkalinity. Values of pH run from 0-14; 7 indicating neutrality, numbers less than 7 indicate increasing acidity, and numbers greater than 7 indicate increasing alkalinity.

Pitting - Surface cavities, may be related to fatigue, overload or corrosion.

Pneumatics - Engineering science pertaining to gaseous pressure and flow.

Poise - Unit of viscosity, defined by the shear stress required to move one layer of fluid along another over a total 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.

Polishing (bore) - Excessive smoothing of the surface finish of the cylinder bore or cylinder liner in an engine to a mirror-like appearance, resulting in depreciation of ring sealing and oil consumption performance.

Polymerization - Chemical combination of similar type molecules to form larger molecules.

Pour Point - An indicator of the ability of an oil or distillate fuel to flow at cool operating temperatures. It is the lowest temperature at which the fluid will flow when cooled under prescribed conditions.

Pour Point Depressant - Additive used to lower the pour point or lower the temperature fluidity of a petroleum product.

Preignition - Ignition of the fuel/air mixture in a gasoline engine before the spark plug fires. Often caused by incandescent fuel or lubricant deposits in the combustion chamber, it wastes power and may damage the engine.

Propylene Glycol - A non-toxic liquid used as a coolant/antifreeze in cooling and heating systems.

Pumpability - The low temperature, low shear stress-shear rate viscosity characteristics of an oil that permit satisfactory flow to and from the engine oil pump and subsequent lubrication of moving components.

Refining - Series of processes to convert crude oil and its fractions into finished petroleum products, which may include thermal cracking, catalytic cracking, polymerization, alkylation, reforming, hydrocracking, hydrofoaming, hydrogenation, hydrogen treating, Hydrofining, solvent extraction, dewaxing, de-oiling, acid treating, clay filtration, deasphalting, etc.

Re-refining - A process of reclaiming used lubricant oils and restoring them to a condition similar to that of virgin stocks by filtration, clay adsorption or more elaborate methods.

Ring Sticking - Freezing of a piston ring in its groove in a piston engine or reciprocating compressor due to heavy deposits in the piston ring zone.

Rust - Slow oxidation of iron.

Rust Preventative - Compound for coating iron surfaces with a film that protects against rust. Commonly used to preserve equipment in storage.

SAE Grade - Numbers applied to automotive lubricants to indicate their viscosity range.

Saybolt, Saybolt Universal Seconds, SUS, or SSU - The most common viscosity measurement prior to the international acceptance of centistokes, SUS measurements are now obsolete. To convert measurements from SUS at 100F to an approximate value in cSt at 40C (ISO viscosity grade), divide the SUS value by 5.

Scoring - Scratches on mechanical parts in the direction of motion caused by abrasive contaminants.

Scuffing - Abnormal engine wear due to localized welding and fracture. It can be prevented through the use of antiwear, extreme-pressure and friction modifier additives. See adhesion.

Semi Fluid - Any substance having attributes of both a liquid and a solid. Similar to semi solid but being more closely related to a liquid than a solid.

Shearing - Relative slipping or sliding between one part of a substance and an adjacent part.

Shear Stability - Ability of a lubricant to withstand shearing forces without being degraded to lower viscosity or consistency.

Sludge - A thick, dark residue, normally of mayonnaise consistency, that accumulates on nonmoving engine interior surfaces. Generally removable by wiping unless baked into a carbonaceous consistency, its formation is associated with insolubles overloading the lubricant.

Solid - Any substance having definite shape that it does not readily relinquish. More generally, any substance in which the force required to produce a deformation depends upon the magnitude of the deformation rather than the rate of deformation.

Stoichiometric - Ratio of fuel to air where the exact proportions for complete reaction of both, with none left over, are present. 

Stoke (St) - Kinematic measurement of a fluids resistance to flow defined by the ratio of the fluids dynamic viscosity to density. 

Supercharger - A device for increasing the pressure and hence the mass of air and fuel burned on each firing stroke. Driven by the crankshaft; therefore, displacement is fixed and directly related to engine RPMs.

Surface Tension - The contractile surface force of a liquid by which it tends to assume a spherical form and to present the least possible surface. It is expressed in dyne/cm or ergs/cm.

Synthetic Lubricant - Fluid made by chemically reacting materials to produce a lube with a specific chemical composition, which has planned, and predictable properties.

Thermally Stable - Ability to withstand temperatures without decomposing. Not to be confused with oxidation stability where oxygen must be present and oxidation rather than decomposition. 

Thickener - The metallic soap or other material used to combine with oil or other lubricating fluid to make a grease.

Torque - The twisting force with which the engines crankshaft actually rotates, measured in foot-pounds.

Total Acid Number (TAN) - The quantity of base, expressed in milligrams, that is required to neutralize all acidic constituents present in one gram of sample.

Total Base Number (TBN) - The quantity of acid, expressed in terms of the number of milligrams that is required to neutralize all basic constituents present in one-gram sample.

Total Solids - The total amount of solids contamination, both suspended and non-suspended present in the lubricant. This test is indicative of carburetion problems (too rich or too lean), if the oil filter has reached the saturation point and is no longer able to remove contamination from the system, and if the air intake system is functioning properly and allowing enough air into the unit for complete burn to take place.

Tribology - Science of the interactions between surfaces moving relative to each other, including the study of lubrication, friction and wear.

Turbine - A device consisting of blades attached to a disc or rotor, which converts flow into rotary action.

Turbocharger - A device for increasing the pressure and hence the mass of air and fuel burned on each firing stroke. A turbine of exhaust gases drives a compressor; therefore, efficiency is variable and related to exhaust pressure.

Vapor Lock - Condition wherein the fuel boils in the fuel system forming bubbles that retard or stop the flow of fuel to the engine.

Varnish - A thin, insoluble, non-wipeable film occurring on interior engine parts.

Viscosity - Measure of a fluids resistance to flow.

Viscosity Index (V.I.) - Relationship of viscosity to temperature of a fluid. High viscosity index fluids tend to display less change in viscosity with temperature than low viscosity index fluids.

Viscosity Index Improver (V.I.I.) - Additive to improve or increase the viscosity index. A VI improver increases an oils resistance to thinning as it is heated. It is commonly used in multi-viscosity or multigrade oils. Since a VI improver increases the viscosity as well as the viscosity index, it must be taken into consideration when formulating oil. (Example: taking an oil in the SAE 30 range, adding a VI improver could give an oil like a SAE 40)

Viscosity Modifier - See V.I.I. Additive, usually a high molecular weight polymer that reduces the tendency of an oils viscosity to change with temperature.

Wear - Damage resulting from the removal of materials from surfaces in relative motion.

Zinc (ZDP) - Commonly used name for zinc dithiophosphate, an antiwear/oxidation inhibitor chemical.