Grease Glossary Terms I Comparative Viscosity Table
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OIL GLOSSARY TERMS
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A
Abrasive Wear - Wear between two surfaces in relative motion due to particles (three body) or surface roughness
(two body).
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Acid Number - A measure of the amount of KOH needed to neutralize all or part of the acidity of a petroleum
product.
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Additive - Any material added to a base stock to change its properties, characteristics or performance.
Adhesive Wear - Wear caused by metal-to-metal contact; characterized by local welding and tearing of the
surface.
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Aniline Point - The lowest temperature at which equal volumes of aniline and hydrocarbon fuel or lubricant
base stock are completely miscible. A measure of the aromatic content of a hydrocarbon blend, used to predict
the solvency of a base stock or the cetane number of a distillate fuel.
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Antifoam Agent - An additive used to suppress the foaming tendency of petroleum products in service.
May be a silicone oil to break up surface bubbles or a polymer to decrease the number of small entrained bubbles.
Antistatic Additive An additive that increases the conductivity of a hydrocarbon fuel to hasten the dissipation of electrostatic charges during high-speed dispensing, thereby reducing the fire/explosion hazard.
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Antiwear Agents - Additives or their reaction products, which form thin, tenacious films on highly loaded parts
to prevent metal-to-metal contact.
Apparent Viscosity - A measure of the viscosity of a non-Newtonian fluid under specified temperature and
shear rate conditions.
Ash - Metallic deposits formed in the combustion chamber and other engine parts during high-temperature
operation.
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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 % by mass.
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Automatic Transmission Fluid (ATF) - Fluid for automatic and hydraulic transmissions in motor vehicles.
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B
Bactericide - Additive to inhibit bacterial growth in the aqueous component of fluids, preventing foul odors.
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.
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Base Number - The amount of acid (perchloric or hydrochloric) needed to neutralize all or part of a lubricant's
basicity, expressed as KOH equivalents.
Base Oil Credit - In lubricant cost calculations, the value of the base fluid displaced by the additive package.
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Base Stock - The base fluid, usually a refined petroleum fraction or a selected synthetic material, into which
additives are blended to produce finished lubricants.
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Bitumen - Also called asphalt or tar, bitumen is the brown or black viscous residue from the vacuum distillation
of crude petroleum. It also occurs in nature as asphalt "lakes" and "tar sands". It consists of high molecular weight hydrocarbons and minor amounts of sulfur and nitrogen compounds.
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Black Oils - Lubricants containing asphaltic materials, which impart extra adhesiveness, that are used for open
gears and steel cables.
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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.
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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 (EP) additives
to prevent metal-to-metal contact.
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Bright Stock - A heavy residual lubricant stock with low pour point, used in finished blends to provide good
bearing film strength, preent scuffing, and reduce oil consumption.
Usually identified by its viscosity, SUS at 210°F or cSt at 100°C.
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Brinelling - Denting caused by impact of one bearing component against another while stationary.
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Bromine Number (Value) - The percentage of bromine that will be absorbed by a chemically unsaturated
substance (base oil, vegetable oil, rubber, etc.) in a given time under arbitrary conditions. A measure of unsaturation.
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Brookfield Viscosity - Measure of apparent viscosity as determined by the Brookfield viscometer at a controlled temperature and shear rate.
C
Cams - Eccentric shafts used in most internal combustion engines to open and close valves.
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Carbon Residue - Coked material remaining after an oil has been exposed to high temperatures under controlled conditions.
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Catalytic Converter - An integral part of vehicle emission control systems since 1975. Oxidizing converters
remove hydrocarbons and carbon monoxide (CO) from exhaust gases, while reducing converters control nitrogen
oxide (NOx) emissions. Both use noble metal (platinum, palladium or rhodium) catalysts that can be "poisoned" by
lead compounds in the fuel or lubricant.
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Cavitation - The formation and subsequent collapse of vaporous cavities within a liquid; caused by movement or vibration within the liquid film.
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Cavitation Damage - An erosion process in which metal is removed by cavitation.
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Centipoise - Measurement unit of absolute (or dynamic) viscosity of a fluid. One centipoise equals 0.01 Poise
and is equivalent to one milliPascal-sec (mPa-s) in SI units. See definition for Poise (in this section) and also in the Viscosity Section.
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CentiStoke - Measurement unit of kinematic viscosity of a fluid. One centiStoke equals 0.01 Stokes and is
equivalent to one mm2/sec in SI units. See definition of Stoke (in this section) and also in the Viscosity Section.
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Cetane Index - A value calculated from the physical properties of a diesel fuel to predict its Cetane Number.
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Cetane Number - A measure of the ignition quality of a diesel fuel, as determined in a standard single cylinder
test engine, which measures ignition delay compared to primary reference fuels. The higher the Cetane Number,
the easier a high-speed, direct-injection engine will start, and the less "white smoking" and "diesel knock" after startup.
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Cetane Number Improver - An additive (usually an organic nitrate) that boosts the Cetane Number of a fuel.
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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.
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Cold Cranking Simulator (CCS) - 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.
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Compression Ratio - In an internal combustion engine, the ratio of the volume of combustion space at bottom
dead center to that at top dead center.
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Copper Strip Corrosion - A qualitative measure of the tendency of a petroleum product to corrode pure
copper.
Corrosion Inhibitor Additive that protects lubricated metal surfaces from chemical attack by water or other contaminants.
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Corrosive Wear - Wear caused by chemical reaction.
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Crown - The top of the piston in an internal combustion engine above the fire ring, exposed to direct flame impingement.
D
Demulsibility - A measure of a fluid's ability to separate from water.
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Denaturants - Toxic or noxious components used in fuel ethanol to make it unfit for use as a beverage.
Density Mass per unit volume.
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Detergent - A substance added to a fuel or lubricant 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.
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Detergent/Dispersant - An additive package that combines a detergent with a dispersant.
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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."
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Dilution of Engine Oil - Contamination of crankcase oil by unburned fuel, leading to reduced viscosity and
flash point. May indicate component wear or fuel system maladjustment.
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Dispersant - An additive that helps keep solid contaminants in a crankcase oil in colloidal suspension, preventing sludge and varnish deposits on engine parts. Usually nonmetallic ("ashless"), and used in combination with detergents.
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Distillation - The basic test used to characterize the volatility of a gasoline or distillate fuel.
E
Elastohydrodynamic Lubrication (EHD) - A lubricant regime 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.
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Emissions (Mobile Sources) - The combustion of fuel leads to the emission of exhaust gases that may be regarded
as pollutants. Water and CO2 are not included in this category but CO, NOx and hydrocarbons are subject to legislative control. All three are emitted by gasoline engines; diesel engines also emit particulates that are controlled.
Emissions (Stationary Sources) - Fuel composition can influence emissions of sulfur oxides and particulates from power stations. Local authorities control the sulfur content of heavy fuel oils used in such applications.
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Emulsifier - Additive that promotes the formation of a stable mixture, or emulsion, of oil and water.
End Point - Highest vapor temperature recorded during a distillation test of a petroleum stock.
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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, carbon, residues from fuel or lubricating oil additives, dust and metal
particles also contribute.
EP Additive (Extreme Pressure Agent) - Lubricant additive that prevents sliding metal surfaces from seizing under extreme pressure conditions.
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EPA Complex Model - More restrictive than the simple model, and contains limits on RVP, oxygen, olefins, benzene, sulfur, and T-90.
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EPA Simple Model - Used to define reformulated gasoline effective January 1, 1995. The model includes RVP and oxygen content requirements to reduce volatile organic compound emissions. It caps oxygen, benzene, sulfur, olefins, and T-90 content at levels equal to or lower than a refiner's 1990 baseline.
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Erosion - Wearing away of a surface by an impinging fluid or solid.
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Exhaust Gas Recirculation (EGR) - System to reduce automotive emission of nitrogen oxides (NOx).
It routes exhaust gases into the carburetor or intake manifold where they dilute the air/fuel mixture and reduce
peak combustion temperatures, thereby reducing the tendency for NOx to form.
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F
False Brinelling - Fretting of one bearing component against another; may appear as a dent, but original surface
finish is worn away.
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Fatigue - Cracking, flaking or spalling of a surface due to stresses beyond the endurance limit of the material.
FAS Free along side.
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Ferrography - Magnetic particle analysis.
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Flash Point - Minimum temperature at which a fluid will support instantaneous combustion (a flash) but before
it will burn continuously (fire point). Flash point is an important indicator of the fire and explosion hazards associated with a petroleum product.
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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.
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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.
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Frost - Field of micropits; form of microadhesive wear.
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Fuel Ethanol - Ethanol (ethyl alcohol, C2H5OH) with impurities, including water but excluding denaturants.
G
Galling - See adhesive wear.
Gaseous Fuels - Liquefied or compressed hydrocarbon gases (propane, butane or natural gas), which are finding increasing use in motor vehicles as replacements for gasoline and diesel fuel.
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Gasoline - A volatile mixture of liquid hydrocarbons, containing small amounts of additives and suitable for
use as a fuel in spark-ignition, internal-combustion engines.
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Gasoline/Ethanol Blend - A spark-ignition automotive engine fuel containing denatured fuel ethanol in a base gasoline. It may be leaded or unleaded.
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Gravity - In petroleum products, the mass/volume relationship expressed as: Mass/unit volume product @
60°F Specific Gravity = ---- Mass/unit volume water @ 60°F 141.5 API Gravity = --- — 131.5 Specific Gravity @ 60°F/60°F
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Gross Additive Treating Cost (GATC) - The cost of additive in one volume unit of finished product not
including base fluid credit or shipping costs.
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Gross Delivered Treating Cost (GDTC) - The cost of additive in one volume unit of finished product including shipping cost, but not base fluid credit.
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H
High Temperature High Shear Rate Viscosity (HTHS) - A measure of a fluid's resistance to flow under
conditions resembling highly-loaded journal bearings in fired internal combustion engines, typically
1 million s-1 at 150°C.
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Hydrofinishing - A process for treating raw extracted base stocks with hydrogen to saturate them for improved stability.
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Hydrolytic Stability - Ability of additives and certain synthetic lubricants to resist chemical decomposition
(hydrolysis) in the presence of water.
I
Induction Period - In an oxidation test, the time period during which oxidation proceeds at a constant and relatively low rate. It ends at the point where oxidation rate increases sharply.
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Inhibitor - Additive that improves the performance of a petroleum product by controlling undesirable chemical reactions, i.e. oxidation inhibitor, rust inhibitor, etc.
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Insolubles - Contaminants found in used oils due to dust, dirt, wear particles or oxidation products.
Often measured as pentane or benzene insolubles to reflect insoluble character.
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Iodine Number (Value) - The percentage of iodine that will be absorbed by a chemically unsaturated substance
(base oil, vegetable oil, rubber, etc.) in a given time under arbitrary conditions. A measure of unsaturation.
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J
K
Kinematic Viscosity - Measure of a fluid's resistance to flow under gravity at a specific temperature
(usually 40°C or 100°C).
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L
Lands - The circumferential areas between the grooves of a piston.
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Lead - Commonly used name for tetraethyl or tetramethyl lead, an additive used in gasoline to improve octane
ratings. Elemental lead is commonly used in sleeve bearing and bushing alloys.
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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.
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M
Morphology - Pertaining to structure and form.
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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.
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N
Naphthenic - A type of petroleum fluid derived from naphthenic crude oil, containing a high proportion of
closed-ring methylene groups.
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Net Additive Treating Cost (NATC) - The cost of additive in one unit of finished product including base
fluid credit, but not shipping costs.
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Net Delivered Treating Cost (NDTC) - The cost of additive in one unit of finished product including base
fluid credit and shipping costs.
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Neutralization Number - A measure of the acidity or alkalinity of an oil. The number is the mass in milligrams
of the amount of acid (HCl) or base (KOH) required to neutralize one gram of oil.
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Neutral Oil - The basis of most commonly used automotive and diesel lubricants, they are light overhead cuts
from vacuum distillation.
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Newtonian Flow - Rheological characteristic of a fluid where the rate of shear is directly proportional to the
shearing force, as with straight grade oils that do not contain a 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 or a soot-laden used engine oil.
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Nitration - The process whereby nitrogen oxides attack petroleum fluids at high temperatures, often resulting in viscosity increase and deposit formation.
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O
1990 Oxygenated Gasoline - Required annually from September 15 to March 15 for use in CO nonattainment
areas. Oxygenated gasoline is defined as a spark-ignition engine fuel meeting ASTM D 4814 specifications and
blended to include a minimum of 2.0% mass oxygen and a maximum of 1.0% volume benzene.
Octane Number - A measure of a fuel's ability to prevent detonation in a spark ignition engine. Measured in a
standard single-cylinder, variable-compression-ratio engine by comparison with primary reference fuels.
Under mild conditions, the engine measures Research Octane Number (RON); under severe conditions Motor
Octane Number (MON). Where the law requires posting of octane numbers on dispensing pumps, the Antiknock
Index (AKI) is used. This is the arithmetic average of RON and MON, (R + M)/2. It approximates the Road Octane Number, which is a measure of how an "average" car responds to the fuel.
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Octane Requirement (OR) - The lowest octane number reference fuel that will allow an engine to run knock-free under standard conditions of service. OR is a characteristic of each individual vehicle.
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Octane Requirement Increase (ORI) - As deposits accumulate in the combustion chamber, the ORI of an
engine increases, usually reaching an equilibrium value after 10,000 to 30,000 km.
ORI is a measure of the increase, which may be in the range of three to ten numbers.
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Oxidation - Occurs when oxygen attacks petroleum 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.
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Oxidation Inhibitor - Substance added in small quantities to a petroleum product to increase its oxidation
resistance, thereby lengthening its service or storage life; also called antioxidant.
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Oxidation Stability - Resistance of a petroleum product to oxidation and, therefore, a measure of its potential
service or storage life.
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Oxygenate - An oxygen containing, ashless organic compound, such as alcohol or ether, that can be used as a
fuel or fuel supplement.
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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 anhydrous ethanol in unleaded gasoline.
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Ozone & CO Nonattainment Areas - Any area of the continental U.S. that does not meet the 1990 Clean Air Act requirements for carbon monoxide or ground-level ozone pollutants.
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P
Paraffinic - A type of petroleum fluid derived from paraffinic crude oil and containing a high proportion of straight chain saturated hydrocarbons. Often susceptible to cold flow problems.
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Percentage Permanent Viscosity Loss (PPVL) - Measure of the PVL related to the viscosity of the fresh oil;
equals PVL divided by fresh oil viscosity, multiplied by 100.
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Percentage Temporary Viscosity Loss (PTVL) - Difference between the viscosity of an oil measured at low
and high shear rates, divided by viscosity measured at low shear rate, multiplied by 100. All viscosities must be
measured at the same temperature and using the same units (CST or cP).
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Permanent Viscosity Loss (PVL) - Irreversible reduction in lubricant viscosity due to mechanical shear in
engines or laboratory test rigs. PVL equals the difference between the fresh oil viscosity and that of the degraded
oil, both measured at the same temperature.
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Pitting Surface cavities - may be related to fatigue, overload or corrosion.
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Plastic Flow - Surface deformation of metal as a result of yielding under heavy load.
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Poise (P) - Measurement unit of a fluid's resistance to flow, i.e., viscosity, 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 stress dynes/cm2 Viscosity = ------------ = --------- = 1 Poise shear rate's
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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.
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Positive Crankcase Ventilation (PCV) - System for removing blow-by gases from the crankcase and returning
them through the carburetor intake manifold to the combustion chamber where the recirculated hydrocarbons are burned. A PC valve controls the flow of gases from the crankcase to reduce hydrocarbon emissions.
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Pour Point - An indicator of the ability of an oil or distillate fuel to flow at cold operating temperatures.
It is the lowest temperature at which the fluid will flow when cooled under prescribed conditions.
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Pour Point Depressant - Additive used to lower the pour point or low-temperature, low shear-rate fluidity of a petroleum product.
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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.
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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.
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Q
R
Refining - Series of processes to convert crude oil and its fractions into finished petroleum products,
including thermal cracking, catalytic cracking, polymerization, alkylation, reforming, hydrocracking, hydroforming, hydrogenation, hydrogen treating, Hydrofining®, solvent extraction, dewaxing, de-oiling, acid treating, clayfiltration
and deasphalting.
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Rerefining - 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.
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Ridging In gear teeth - A form of plastic flow characterized by a rippled appearance on the surface.
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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.
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Rings - Circular metallic elements that ride in the grooves of a piston and provide compression sealing during combustion. Also used to spread oil for lubrication.
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Rolling and Peening - In gear teeth, a form of plastic flow that gives the surface a hammered appearance;
metal may be rolled over the teeth tips.
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Rust Preventative - Compound for coating metal surfaces with a film that protects against rust.
Commonly used to preserve equipment in storage.
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S
Scratching - Fine abrasive furrows in the direction of sliding.
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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.
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SEM - Scanning electron microscope.
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Shear Stability Index (SSI) - A measure of an oil's irreversible viscosity loss attributable to the viscosity modifier
when the oil is subjected to engine operation or special test conditions. Also sometimes called Permanent Shear
Stability Index (PSSI), SSI is defined by the equation: SSI = 100(Vo-Vs)/(Vo-Vb), where Vo = viscosity of the
unsheared oil, Vs = viscosity of the sheared oil, and Vb = viscosity of the base oil.
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Sludge - A thick, dark residue, normally of mayonnaise consistency, that accumulates on nonmoving engine
interior surfaces. Generally removable by wiping unless baked to a carbonaceous consistency, its formation is
associated with insolubles overloading of the lubricant.
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Solvent Extraction - Refining process used to separate reactive components (unsaturated hydrocarbons)
from lubricant distillates in order to improve the oil's oxidation stability, viscosity index and additive response.
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Solvent Refining - A process for extracting lubricant base stocks from stripped heavy gas oil or other heavy,
stripped crude stream using selective solvents such as furfural or phenol.
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Spalling - Severe damage characterized by large pits, cavities and related cracks; related to overload and fatigue.
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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 mm2/s.
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Synthetic Lubricant - Lubricating fluid made by chemically reacting materials of a specific chemical composition
to produce a compound with planned and predictable properties.
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T
Temporary Shear Stability Index (TSSI) - The measure of the viscosity modifier's contribution to an oil's
percentage viscosity loss under high shear conditions.
Temporary Shear Loss (TSL) - results from the reversible lowering of viscosity in high shear areas of the engine,
an effect that can positively influence fuel economy and cold cranking speed.
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Temporary Viscosity Loss (TVL) - Difference between dynamic viscosity measured at high shear rate compared
to that determined at low shear rate. Both viscosities are measured at the same temperature.
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Tribology - Science of the interactions between surfaces moving relative to each other, including the study
of lubrication, friction and wear.
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U
V
Valve Lifter - Sometimes called a "cam follower," a component in engine designs that use a linkage system
between a cam and the valve it operates. The lifter typically translates the rotational motion of the cam to a
reciprocating linear motion in the linkage system.
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Vapor Pressure-Reid (RVP) - Measure of the pressure of vapor accumulated above a sample of gasoline or
other volatile fuel in a standard bomb at 100°F (37.8°C). Used to predict the vapor locking tendencies of the fuel
in a vehicle's fuel system. Controlled by law in some areas to limit air pollution from hydrocarbon evaporation while dispensing.
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Varnish - A thin, insoluble, nonwipeable film occurring on interior engine parts. Can cause sticking and malfunction
of close-clearance moving parts. Called lacquer in diesel engines.
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Viscosity - A measure of a fluid's resistance to flow.
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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.
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Viscosity Modifier - Lubricant additive, usually a polymer, whose function is to provide beneficial rheological properties to lubricating oils, such as reducing the tendency of an oil's viscosity to change with temperature.
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W
White Oil - Highly refined lubricant stock used for specialty applications such as cosmetics and medicines.
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X
Y
Z
Zinc (ZDP) - Commonly used name for zinc dithiophosphate, an antiwear/oxidation inhibitor chemical.
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