A substance capable of reducing the friction between two sliding surfaces.

It reduces the wear on the parts involved and decreases the working temperature. Its main effect is therefore a saving in energy.

Liquid (motor, transmission and industrial, etc. oils) Semisolid (pastes and greases with different consistencies and compositions) Solid (Graphite, Molybdenum disulphide, Micronised copper, etc)

It is a mixture of base oils (70-99%) and additives (1-30%)

It is the main component that determines the basic lubrication and viscosity characteristics.

Mineral oils: Mixture of hydrocarbons distilled from petroleum. These are obtained in refineries and are classified according to their purity as Group I or II. Hydrocracked oils: Hydrocarbons obtained by special processes with hydrogenation are classified as Group III. Synthetic oils: Those oils obtained by the process of synthesising materials derived from petroleum or other raw materials. These are classified as Group IV (PAOs, polyalphaolefins) and as Group V (others: esters, polybutenes, alkylbenzenes, polyethers, alkylene glycols, etc).

Colour, density, viscosity, viscosity index, flash point, freezing point, carbonaceous residue, sulphur content, oxidation stability, copper corrosion, demulsibility.

VISCOSITY. Depending on the application and working temperature, correct choice of viscosity allows for a thick enough lubricant film to provide a maximum reduction in friction.

This is a measurement of a liquid’s resistance to flow. It should not be confused with density, which is the ratio between weight and volume. Oil is more viscous than water, but water is denser. This is why oil and most petroleum derivatives float on water.

It is measured in viscosimeters. The most commonly used units are ISO levels (centistokes, cSt at 40 ºC), SUS levels (Saybolt Universal Seconds), SAE J300 levels for engine oils (SAE 5W, 10W, 15W, 20, 30, 40, 50) and SAE J306 levels for gears (SAE 75W, 80, 90, 140, 250). Units of viscosity always refer to a specific temperature.

A liquid’s viscosity decreases as temperature increases. The Viscosity Index is a number that measures the change in viscosity with temperature. The higher the index, the more resistant the liquid is to changing its viscosity because of the effects of temperature. The most commonly used mineral oils have a VI of 90-100 (e.g. single-grade and hydraulic motor oils). Multigrade oils (e.g. 20W-50, 15W40, 5W40) have an VI of 120-180.

These are chemical compounds that are added to base oils to improve their properties or to give them additional properties necessary for the application for which the oil is to be used.

Viscosity Index Improvers enhance viscosity. Freezing Point Depressants lower the freezing point. Antioxidants extend the oil’s life. Anti-corrosion agents protect the non-ferrous metal parts to be lubricated. Anti-rust agents protect iron parts. Detergents neutralise the acids formed in combustion. Dispersants prevent particles from caking and precipitating. Anti-foaming agents prevent the formation of foam. Anti-wear agents reduce friction in severe working conditions.

This is the Total Base Number or the alkaline reserve an oil has to neutralise the acids formed during the combustion and degradation of the components of the fuel and the lubricant. The TBN is provided by the detergent additive.

It is an oil with a high Viscosity Index. Variation in viscosity with temperature is lower than for a single-grade oil. It is suitable for working at low and high temperatures. A SAE 15W40 motor oil for example.

This is not a description of the level of quality. It defines only the viscosity level in accordance with the SAE J300 standard for motor oils. 15W refers to the viscosity at low temperatures (W stands for “winter) and the digits 40 refer to viscosity at high temperatures (100 ºC). SAE is the Society of Automotive Engineers (USA).

International organisations such as API, ACEA, JASO, and ILSAC, etc., (for motor oils) and DIN, ISO, USS, etc., (for industrial oils). Motor, machinery and equipment manufacturers such as MB, VOLVO, VW, MAN, CATERPILLAR, JOHN DEERE, FORD, ATLAS-COPCO, VICKERS, FENDER, etc.

API stands for American Petroleum Institute, an association that defines quality standards for motor oils, particularly for the American market. Quality standards are defined using two letters. The first refers to whether the product is for gasoline (S) or for diesel (C) and the second letter indicates the standard of quality and runs in ascending alphabetic order. Hence, SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL are used in ascending order for gasoline and CA, CB, CC, CD, CE, CF, CF+, CF4, CG4, CH4, CI4 are used for diesel. If an oil is assigned the both letters for gasoline and diesel, it is suitable for the two types of engines in the levels of quality required. The oil API SL/CI4 therefore fulfils the two strictest quality standards for gasoline and diesel.

ACEA, which stands for the European Automobile Manufacturers Association, establishes standards of quality and classifies motor lubricants, mainly for Europe. These are classified as follows:

As with motor oils, API classifies engine gear oils (for gear boxes and differentials) as API GL-1 and GL-2 for light service, GL-3 for moderate service, GL-4 for severe service and GL-5 for very severe service.

The terms Super Tractor Oil Universal and Universal Transmission Tractor Oil are used by the manufacturers of agricultural machinery for multifunctional lubricants. STOU is suitable for engines, transmissions, hydraulics and brakes and UTTO can be used for all of these except engines.

• API classification: TA, TB, TC
• JASO classification (Japanese Automobile Standards Organisation):
  • JASO FA: low quality level.
  • JASO FB: minimum acceptable quality level.
  • JASO FC: manufacturer quality, low in smoke.
• ISO classification (International Organisation for Standardisation):
  • ISO-L-EGD
  • ISO-L-EGE

Very strict Piaggio Hexagon standard for scooters with separate lubrication.

All motor oils can be mixed (mineral or synthetic for gasoline or diesel) and quality will not decrease if they have the same specifications. Viscosities can also be mixed to produce a viscosity that is not the mean of both oils but rather more similar to the oil with the lower viscosity. Lubricants for different applications should not be mixed. Industrial lubricants should be analysed by an expert prior to mixing to determine whether or not they are compatible.

If they have similar API or ACEA quality levels, the mineral oil may, in principal, be used. The advantages of synthetic oil lie in its greater protection against wear upon ignition, the oil’s longer working life and, above all, its compliance with new environmental requirements. These requirements demand a reduction in fuel consumption and a reduction in pollution through the formation of less particles and waste.

En principio si tienen niveles de calidad API, ACEA que son parecidos, podemos utilizar el mineral. Las ventajas del sintético están en la mayor protección al desgaste en el arranque, la mayor duración del aceite y sobre todo, en que cumplen las nuevas exigencias medioambientales como son: reducir el consumo de combustible y reducir la contaminación por la menor formación de partículas y residuos.

Used oil is considered to be toxic waste and is governed by legislation that must be complied with (BOE —Spanish Official Gazette— of 28 February 1989). It must be deposited in special containers or at automobile workshops for collection and treatment by an authorised manager. It must not be discharged into the ground under any circumstances.