Any substance, containing hydrogen in combination with a nonmetallic element, capable of producing hydrogen ions in a solution. An acid is capable of neutralising or being neutralised by a base.

A test using potassium hydroxide as the neutralizing agent to measure the acidity of an oil. The result is measured in milligrams of potassium hydroxide needed to neutralize one gram of oil.

Acidity denotes the presence of acidic constituents. Its concentration defines the acid number.

A chemical added in small quantities to a base fluid in order to improve specific properties of the lubricant, such as fluid life, lubricity, wear protection and rust protection.

The lowest temperature at which a hydrocarbon fluid is completely miscible with an equal quantity of aniline. The higher the reading, the lower the aromatic content, and the smaller the effect on rubber.

An additive used to suppress the foaming tendency of petroleum products in service. Either a silicone oil to break up surface bubbles, or a polymer to decrease the number of small entrained bubbles.

A chemical added in small quantities to a petroleum product to increase its oxidative resistance in order to extend its service life.

Additives or their reaction products which form thin, tenacious films on highly loaded parts to prevent metal-to-metal contact.

Some additives, particularly conventional detergent additives, leave behind a powdery residue after combustion. This residue, known as ash, can cause engine malfunction if allowed to build up in the combustion chamber, cylinder liner ports and turbochargers.

The ash content of an oil, determined by charring the oil and breaking the residue with sulphuric acid and evaporating to dryness.

Microscopic protrusion on a metal surface that typically occurs with normal finishing processes. Lubrication should be sufficient to prevent asperities on each metal surface from protruding through the lubricant film and making contact with other metal surfaces.

Minimum temperature at which a combustible fluid will burst into flame without any extraneous ignition source. This temperature is typically several hundred degrees higher than the flash and fire point.

A compound which reacts with an acid to produce salt and water.

The formation of blisters on the surface of a seal face, degrading it and increasing leak rates and friction, and increasing the potential for the seal shaft to fail.

Refined petroleum oil used in the production of lubricants. The base stock may be used alone or blended with other base stocks and/or additives, to manufacture a finished lubricant.

The mixing of various components, including base oils and additives, in the preparation of a lubricant with specified properties.

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 to prevent metal-to-metal contact.

Eccentric lobes attached to a camshaft and driven by a crankshaft which are used in most internal combustion engines to open and close valves and sometimes operate fuel pumps.

Coked material formed after lubricating oil has been exposed to high temperatures. Many consider the type of carbon formed to be of greater significance that the quantity.

The formation of bubble of air or vapor in a liquid, resulting from the swift movement of a solid object (such as a propeller or piston) through the liquid. Also, the pitting and wearing away of metal or other solid surfaces caused by the collapse of air/vapor pockets in surrounding liquid.

The temperature at which a cloud or haze begins to appear when an oil, which has been previously dried, is cooled under prescribed conditions. Such a cloud or haze is usually due to the separation of wax from the oil.

The decay and loss of metal caused by a chemical reaction between the metal and another substance, such as contaminants in a lubricant.

A substance added to a lubricant to protect against metal corrosion.

The top of the piston in an internal combustion engine above the fire ring, exposed to direct flame impingement.

Lubricants having a high Base Number (BN) for the lubrication of the cylinders of crosshead marine diesel engines and some types of trunk piston engines.

A lubricant’s ability to separate from water.

An additive which chemically neutralizes acidic contaminants in the oil before they become insoluble and fall out of the oil to form sludge. Particles are kept finely divided so that they can remain dispersed throughout the lubricant.

An additive that keeps insoluble contaminants dispersed (colloidally suspended) in a lubricant, preventing the particles from settling and accumulating. Dispersants help prevent the buildup of sludge, varnish and other deposits.

The temperature at which grease passes from a semisolid state to a liquid state under specific test conditions.

Generally used for the transportation and storage of lubricants, a drum has a nominal volume of 208 litres (55 US gal; 46 imp gal) and measures 880 millimetres (35 in) tall with a diameter of 610 millimetres (24 in).

An additive that promotes the mixing of water and oil to form an intimate mixture called an emulsion. Emulsions generally have a cloudy or milky appearance.

Describing a state of an immiscible fluid component. Minute quantities of a fluid (typically water) can be dissolved or absorbed into the oil, but excess quantities can be most harmful to equipment due to the entrainment leaving gaps in the lubricated areas.

A chemical compound typically formed through the reaction between an acid and an alcohol.

An additive that prevents sliding metal surfaces from seizing in extreme-pressure conditions. It combines chemically with metal surfaces to form a layer of film that prevents welding and excessive wear of contacting metal parts under shock load.

Lowest temperature at which a combustible fluid will burst into flame in the presence of an extraneous ignition source. Very little additional heat is required to reach the fire point from the flash point.

Lowest temperature at which vapor from a sample of a petroleum product or other combustible fluid will “flash” in the presence of an ignition source. The flash can be seen in the form of a small spark over the liquid.

An additive which causes foam to dissipate more rapidly. It promotes the combination of small bubbles into large bubbles which burst more easily.

A possible reaction of an oil when mixed with air. This entrained air can result in reduced film strength and a performance reduction.

Resistance to motion on a surface or by a substance as a result of its contact with another surface or substance. Sliding friction is that which occurs between two solid bodies, while fluid friction is that which occurs between the molecules of a fluid in motion. Both types of friction can be wasteful in power and energy, and sliding friction causes wear.

A type of lubricant composed of lubricant oils thickened with a material that contributes a degree of plasticity (typically soaps). Just as viscosity is the basic property of lubricating oil, consistency is the basic property of grease. Consistency is measured in terms of penetration, tested in terms of tenths of a millimeter that a standard cone acting under the influence of gravity penetrates the sample under controlled test conditions. The greater penetration, the softer the grease.

An Intermediate Bulk Container (IBC) is a reusable industrial container designed for the transport and storage of lubricant. ntermediate bulk containers are stackable containers mounted on a pallet.  The most common sizes are 1,040 liters / 275 U.S. gallons.

Any oil derived from a mineral source, such as petroleum.

Capable of being mixed in any concentration without separation of phases.

Asphaltic or “sour” crude oil. It has poor low-temperature fluidity as a result of a low viscosity index. It has good solvency properties.

An indication of the acidity or basicity (alkalinity) of an oil. The neutralization number is expressed in milligrams of potassium hydroxide or hydrochloric acid needed to neutralize any acid or base in one gram of oil. The Acid Number (AN) test uses potassium hydroxide as the neutralizing agent, and the Base Number (BN) test uses hydrochloric acid as the neutralizing agent.

A form of chemical deterioration to which oil products are subject to, and involves the addition of oxygen atoms resulting in degradation. It is accelerated by higher temperatures above 71,12°C / 160°F, with the rate of oxidation doubling by each 6,67°C / 20°F increase. Oxidation produces sludge, varnish, gum and acid, all of which are undesirable.

A widely used low-temperature flow indicator, depicted as 5°F above the temperature to which a lubricant maintains fluidity. It is a significant factor in cold-weather start-up.

A lubricant additive for protecting iron and steel components from rusting caused by water contamination or other harmful materials from oil degradation. Some rust inhibitors operate similarly to corrosion inhibitors by forming inert films on metal surfaces. Other rust inhibitors absorb water by incorporating it into a water-in-oil emulsion so that only oil touches the metal surfaces.

Generic term for contamination in a lubricated system and on parts bathed by the lubricating oil. This includes decomposition products from the fuel, oil and particulates from sources external to the system.

The ability to dissolve into a solution producing a homogeneous physical mixture. The degree of solvency varies along with the rate of dissolution depending on the amount of heat added to the solution.

Measure of a fluid’s resistance to flow. This is typically measured as the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid. Viscosity varies inversely with temperature, so the measurements are always expressed together. Tests are typically conducted at 40°C and 100°C.

Lubricant viscosity is measured by three main standards. The most familiar is Society of Automotive Engineers (SAE), next International Standardization Organization (ISO or ISO VG), and finally American Gear Manufacturers Association (AGMA). 

The standardization institutes ISO (International Standards Organization), ASTM (American Society for Testing and Materials), DIN (Deutsches Institut für Normung = German Institute for Standardization), and others created a common viscosity classification. The result is known as the International Standards Organisation Viscosity Grade - ISO VG.

This classification applies mainly for use with industrial lubrication. The viscosity of each grade ranges ± 10 % from the mid-point. The step inbetween two subsequent viscosity grades is approx. 50 % of the lower one. The temperature of 40 °C is related to the operating temperature in machinery.

The viscosity grade of a lubricant oil is also determined by the Society of Automotive Engineers (SAE). Oils can be separated into multigrade oils and monograde oils. Multigrade oils must fulfill two viscosity specifications, their viscosity grade consists of two numbers, e.g. 10W-40: 10W refers to the low-temperature viscosity ("Winter"), 40 refers to the high-temperature viscosity ("Summer"). Currently, most automotive engine oils are multigrade oils, while oils for restricted usage, e.g. for seasonally used engines like lawn mowers, are often monograde oils. While the two numbers specify the SAE viscosity grade, the viscosity index shows the temperature related change of viscosity.

The measure of the rate of change of viscosity with temperature. Heating tends to make lubricants thinner; cooling makes them thicker. The higher the viscosity index is on a particular fluid, the less of a change in viscosity there will be over a given temperature range. In determining the viscosity index, two temperatures of viscosity are taken, one at 40°C and the other at 100°C.