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Lubricants – Glossary of terms

SAE

The Society of Automotive Engineers, usually abbreviated as SAE, has established a numerical code system for grading motor oils according to their kinematic viscosity. SAE viscosity grades include the following: 0, 5, 10, 15, 20, 25, 30, 40, 50 or 60. Some of the numbers can be suffixed with the letter W, designating their "winter" or cold-start viscosity, at lower temperature.

Viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice, at standard temperature. The longer it takes, the higher the viscosity, and thus higher SAE code.

Note that SAE operate a separate viscosity rating system for transmission oils which should not be confused with engine oil viscosity. The higher numbers of a transmission oil (e.g. 75W-140) do not mean that it is necessarily higher viscosity than an engine oil.

Single-grade lubricants

For single-grade oils, the kinematic viscosity is measured at a reference temperature of 100_C (212_F) in units of mm_/s or the equivalent older non-SI units, centistokes (abbreviated cSt). Based on the range of viscosity the oil falls in at that temperature, the oil is graded as an SAE number 0, 5, 10, 20, 30, 40, 50, or 60. The higher the viscosity, the higher the SAE grade number is. The reference temperature is meant to approximate the operating temperature to which motor oil is exposed in an engine.

The viscosity of single-grade oil derived from petroleum without the addition of additives changes considerably with temperature. As the temperature increases, the viscosity of the oil decreases.

On single-grade oils, viscosity testing can be done at cold, winter (W) temperature (as well as checking minimum viscosity at 100_C or 212_F) to grade an oil as SAE number 0W, 5W, 10W, 15W, 20W, or 25W. Single-grade oil graded at the hot temperature is expected to test into the corresponding grade at the winter temperature; i.e. 10 grade oil should correspond to 10W oil. For some applications, such as when the temperature ranges in use are not very wide, single-grade motor oil is satisfactory; for example, lawn mower engines, and vintage or classic cars.

Multi-grade lubricants

The temperature range the oil is exposed to in most vehicles can be wide, ranging from cold ambient temperatures in the winter before the vehicle is started up to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. A specific oil will have high viscosity when cold and low viscosity at the engines operating temperature. The difference in viscosities for any single-grade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers, or VI’s are added to the oil. These additives make the oil a multi-grade motor oil. The idea is to cause the multi-grade oil to have the viscosity of the base number when cold and the viscosity of second number when hot. This enables one type of oil to be generally used all year, and when multi-grades were initially developed, they were frequently described as all-season oil. The viscosity of multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened. The rate at which the oil changes with temperature depends on the ratio of additives to base oil.

The SAE designation for multi-grade oils includes two grade numbers; for example, 10W-30 designates a common multi-grade oil. Historically, the first number associated with the “W” is not rated at any single temperature. The "10W" means that this oil can be pumped by your engine as well as a single-grade SAE 10 oil. "5W" can be pumped at a lower temperature than "10W" and "0W" can be pumped at a lower temperature than "5W". The second number, 30, means that the viscosity of this multi-grade oil at 100_C (212_F) operating temperature corresponds to the viscosity of a single-grade 30 oil at same temperature. The governing SAE standard is called SAE J300. This "classic" method of defining the "W" rating has since been replaced with a more technical test where a "cold crank simulator" is used at increasingly lowered temps. A 0W oil is tested at -35_C, a 5W at -30_C and a 10W is tested at -25_C.

The motor oil grade and viscosity to be used in any given vehicle is specified by the manufacturer of the vehicle, but can vary from country to country when climatic or mpg constraints come into play.

American Petroleum Institute

The American Petroleum Institute (API) Engine Service Classification System was developed as a result of a co-operative effort in the USA between the API, the American Society for Testing Materials (ASTM) and the Society of Automotive Engineers (SAE).

The system defines classes of service for automotive petrol and diesel engine applications as well as stipulating the accepted engine tests (e.g. the various ‘sequence’ tests) or specifications to which each class is related.

The system uses letter designations for each service class, petrol engine service and diesel engine service.

This provides a convenient means for the engine manufacturer to indicate the service characteristics of his various designs, and hence their lubrication requirements.

Similarly the oil suppliers can use the letter designations to indicate for which class or classes of service particular oil is suitable.

Oils suitable for mixed fleets are double classified as, for example, API CD/SE and vice versa.

API Classifications – Petrol Engine Oils

SA: Straight mineral oil with no additives. Prior to 1930.
SB: Mineral oil with some anti-wear and anti-oxidant additives for mild operating conditions. Current 1930 - 1963.
SC: Provides control of high and low temperature deposits, wear, rust and corrosion. Covered engines operating under manufacturers’ warranties in period 1964 - 1968.
SD: Increased protection over SC oils. Meets Ford M2C-101-B and GM6051M specifications. Covered engines current in 1968 - 1971.
SE: Provides high-temperature anti-oxidation, low-temperature anti-sludge and anti-rust performance. Met American manufacturers’ warranty requirements for all naturally aspirated engines in the period 1972 - 1979. Compares to Ford SSM-2C-9011AA, GM6136M and US MIL-46152A specifications.
SF: Introduced in 1980 to give increased high-temperature protection and designed to cope with the additional demands imposed by turbo-charged engines. Meets Ford SSM-2C-9011A, GM-6048M and MIL-L-46152B.
SG: Improved performance over SF, particularly in the prevention of ‘black sludge’ in high performance engines. Introduced in 1989, it also meets MIL-L-46152B, C and D.
SH: Improved performance over SG, which it is intended to replace, in the areas of deposit control, oil oxidation, wear, rust and corrosion. Introduced in 1994.
SJ: Introduced in 1997 and oils meeting SJ requirements have been tested according to the Chemical Manufacturers Association (CMA) Product Approval Code of Practice and may utilise the API Base Oil Interchange and Viscosity Grade Engine Testing Guidelines. They may be used where API SH and earlier categories are recommended.
SL: For all automotive engines presently in use. Introduced July 2001.
SL oils are designed to provide better high-temperature deposit control and lower oil consumption. Some of these oils may also meet the latest ILSAC specification and / or qualify as energy conserving.

API Classifications – Diesel Engine Oils

CA: Dates back to the 1940’s and covers low rated engines using low-sulphur fuel. Compares to MIL-L-2104A and DEF 2101A.
CB: Introduced in 1949 for low rated engines with higher levels of sulphur in the fuel. Often referred to as a supplement 1 oil, meeting DEF 2101D.
CC: Introduced in 1961 for naturally aspirated diesels and also turbo-charged units operating under moderate conditions, where low sulphur fuel is in use. Meets MIL-L-2104B.
CD: Introduced in 1975 and covers turbocharged diesel engines operating under severe conditions with higher levels of sulphur in the fuel. Often referred to as a Series 3 since it meets Caterpillar Series 3 specification together with MIL-L-2104C and D.
CD-II: Introduced for two-stroke diesel engines requiring highly effective control of wear and deposits. Also meets the performance requirements of CD oils.
CE: Introduced in 1983 for certain turbocharged or supercharged heavy duty diesel engines, manufactured since 1983 and operated under both low-speed, high-load and high-speed, high-load conditions.
CF-4: Introduce in 1990 for high-speed, four stroke diesel engines. Particularly suited for on-highway, heavy duty truck applications.
CF: Introduced in 1994 for indirect-injected diesel engines, including those using fuel with high sulphur content.
CF-2: For service typical of two-stroke diesel engines requiring highly effective control over cylinder and ring-face scuffing and deposits. Introduced in 1994 and may also be used where API CF-II oils are recommended.
CG-4: Describes oils for use in high-speed four-stroke diesel engines in both heavy duty on and off-highway applications. Introduced in 1994 these oils are effective in engines designed to meet 1994 exhaust emission standards.
CH-4: Introduced in 1998 for high speed four stroke engines designated to meet 1998 exhaust emissions standards. CH-4 oils are specifically compounded for use with diesel fuels ranging in sulphur content up to 0.5% weight. Can be used in place of CD, CE, CF-4 and CG-4 Oils.
CI-4: Introduced September 2002 for high speed four stroke diesel engines designated to meet 2004 exhaust emission standards implemented in 2002. CI-4 oils are formulated to sustain engine durability where exhaust gas recirculation (EGR) is used and are intended for use with diesel fuels ranging in sulphur content up to 0.5% weight. Can be used in place of CD, CE, CF-4 and Ch-4 engine oils.

API Classifications – Automotive Gear Oils

GL-1: Straight mineral oil, applications - truck manual transmissions.
GL-2: Usually contains fatty materials, applications - worm gear drives, industrial gear oils.
GL-3: Contains mild EP additives, applications - manual transmissions and spiral bevel final drives.
GL-4: Equivalent to the obsolete MIL-L-2105; applications - manual transmissions, and spiral bevel and hypoid gears in moderate service.
GL-5: Virtually equivalent to present MIL-L-2105D; primary field service recommendation of most passenger car and truck builders world-wide. Applications - moderate and severe service in hypoid and other types of gears. May also be used in manual transmissions.
GL-6: Obsolete.

ACEA

The ACEA (Association des Constructeurs EuropÈens dAutomobiles) is officially translated as the European Automobile Manufacturers Association. As its name implies, ACEA is the authorised trade association of the European motor manufacturers and its job essentially is to serve and represent the corporate interests of its members. This involves the need to establish with its members common attitudes, codes of practice, standards etc.

ILSAC

The International Lubricant Standardization and Approval Committee (ILSAC) also have standards for motor oil. Their latest standard was approved in 2004. A key test is the Sequence IIIG, which involves running a 3.8L, GM 3.8L V-6 at 125†horsepower, 3600†rpm, and 150_C oil temperature for 100 hours.

These are much more severe conditions than any API-specified oil was designed for: cars which typically push their oil temperature consistently above 100_C are most turbo-charged engines, along with most engines of European or Japanese origin, particularly small capacity, high power output.

JASO

The Japanese Automotive Standards Organization (JASO) has come up with their own set of performance and quality standards for petrol engines of Japanese origin.

For 4-stroke gasoline engines, the JASO T903 standard is used, and is particularly relevant to motorcycle engines. The JASO T903-MA and MA2 standards are approved wet clutch use, and the JASO T903-MB standard is not suitable for wet clutch use.

For 2-stroke gasoline engines, the JASO M345 (FA, FB, FC) standard is used, and this refers particularly low ash, lubricity, detergency, low smoke and exhaust blocking.

These standards, especially JASO-MA and JASO-FC are designed to address oil-requirement issues not addressed by the API service categories.

OEM

By the early 1990s, many of the European original equipment manufacturer (OEM) car manufacturers felt that the direction of the American API oil standards were not compatible with their own European designed high performance engines. Furthermore, the American "synthetic" way forward was the development of hydro cracking group I/II/III base stocks, whereas the demands of European engines were favouring synthetics from group IV and group V base stocks. As a result many leading European motor manufacturers created and developed their own "OEM" oil standards.

Probably the most well known of these are the VW50*.0* series from Volkswagen Group, and the MB22*.** from Mercedes-Benz. Other European OEM standards are from General Motors, for the Vauxhall, Opel and Saab brands, the Ford "WSS" standards, BMW Special Oils and BMW Long life standards, Porsche, and the PSA Group of Peugeot and CitroÎn.

As a result of this development in oil technology, and the subsequent development of the engines themselves (particularly with powerful engine electronic ECUs), virtually all modern European cars will demand a specific OEM-only oil standard. As a result, they now invariably make no reference at all to API standards, or SAE viscosity grades. They may also make no primary reference to the ACEA standards, with the exception of being able to use a "lesser" ACEA grade oil for "emergency top-up", though this usually has strict limits, often up to a maximum of _ a litre of non-OEM oil.

Additives

In addition to the viscosity index improvers, motor oil manufacturers often include other additives such as detergents and dispersants to help keep the engine clean by minimizing sludge build-up, corrosion inhibitors, and alkaline additives to neutralize acidic oxidation products of the oil. Most commercial oils have a minimal amount of zinc dialkyldithiophosphate as an anti-wear additive to protect contacting metal surfaces with zinc and other compounds in case of metal to metal contact. The quantity of zinc dialkyldithiophosphate is limited to minimize adverse effect on catalytic converters.

Other additives include zinc dialkyldithiophosphate (ZDDP) additives, which typically also contain calcium, are available to consumers for additional protection under extreme-pressure conditions or in heavy duty performance situations. ZDDP and calcium additives are also added to protect motor oil from oxidative breakdown and to prevent the formation of sludge and varnish deposits.

Synthetic oils and synthetic blends

Synthetic lubricants are designed for "long life" extended drain intervals. Instead of making motor oil with the conventional petroleum base, "true" synthetic oil base stocks are artificially synthesized. Synthetic oils are derived from either Group III mineral base oils, Group IV, or Group V non-mineral bases. True synthetics include classes of lubricants like synthetic esters and polyalpha-olefins. Higher purity and therefore better property control theoretically means synthetic oil has good mechanical properties at extremes of high and low temperatures. The molecules are made large and "soft" enough to retain good viscosity at higher temperatures, yet branched molecular structures interfere with solidification and therefore allow flow at lower temperatures. Thus, although the viscosity still decreases as temperature increases, these synthetic motor oils have a much improved viscosity index over the traditional petroleum base. Their specially designed properties allow a wider temperature range at higher and lower temperatures and often include a lower pour point. With their improved viscosity index, true synthetic oils need little or no viscosity index improvers, which are the oil components most vulnerable to thermal and mechanical degradation as the oil ages, and thus they do not degrade as quickly as traditional motor oils.

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