Lubricating oil

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Two lubricating vases as containers for lubricating oil on a machine

Lubricating oils are the most important technical lubricants . They are used to reduce friction , which causes noise and especially wear. In addition, lubricating oil also serves to dissipate heat. Lubricating oil forms a sliding film between moving surfaces, for example in a hinge ; More on this in the article on lubrication .

In demanding environments that are exposed to rain or dust, for example, lubricating greases are used , which can shield the bearing points or roller bearings from external influences and remain at the lubricating point for longer because they are more viscous (more viscous).


Motor oils

motor oil
Main article: Motor oil

With around 50% of the total amount in Europe and around 32% in Germany, motor oil represents the largest single group of lubricants; the total amount has stagnated since about 2001 at around 344,000 t per year. They are used in almost all cars and trucks .

Internal combustion engines place high demands on engine oil. The engine oil is not just a lubricant, but has other important tasks:

  • Transmission of forces (hydraulic in chain tensioners and tappets)
  • Wear protection (of the engine parts moving against each other)
  • Corrosion protection of the engine parts against aggressive combustion products through the formation of protective layers on the metal surface
  • Sealing (the combustion chamber to the crankcase, the intake and exhaust channels via the valve guides to the valve train)
  • Cooling (mainly pistons and crankshaft)
  • Neutralization of acidic combustion products through chemical conversion
  • Cleaning of engine parts by dissolving combustion residues (and aging products in engine oil) with oil-soluble soaps
  • Dispersion of solid foreign matter, dust, abrasion, combustion products such as soot or ash

In order to be able to fulfill these tasks, various requirements are placed on the engine oil, which are characterized by chemical, physical and technological properties. These properties are simplified:

In addition, the following requirements are placed on the engine oil:

  • Neutral behavior towards sealing materials
  • Little tendency to foam
  • Long service life, long oil change intervals
  • Low oil consumption
  • Low fuel consumption
  • Fuel compatibility
  • Environmental sustainability


Mineral oils

Modern four-stroke engine oils are usually mineral or synthetic base oils with an additive package . The base oil is the oil , a petroleum distillate . Since oils have such a high boiling point that they would normally decompose during distillation, this is done under vacuum (see vacuum distillation ). This lowers the boiling point so that temperatures of a maximum of 350 ° C are sufficient. The distillates are then filtered, clarified and refined, among other things, so that an unalloyed oil with a certain viscosity is obtained. This oil is not a pure substance, but a fraction , i.e. a mixture of different hydrocarbons with a similar boiling range. For a long time, these oils were the only oils used in motor vehicles, today they are still available from some manufacturers as compressor oil or machine oil (very old engines (pre-war machines) need these oils because their sealing materials are often not compatible with modern additives).

Up until the 1940s and thereafter, highly stressed engines (especially motorcycle racing engines) were also lubricated with vegetable oil ( castor oil ); the Castrol company has earned its reputation with such oils. Castor oil is called castor oil in English .

In the past, various means were offered which were supposed to improve the oil quality of mineral oils; some of them still exist today. In addition to solid-state additives such as molybdenum disulphide and colloid graphite ( spheroidal graphite ), there were also various chemical additives, some of which served their purpose quite well. Around the 1940s, oils came onto the market that were equipped with such additives as standard and were marketed as HD oils ( heavy duty ).

Synthetic oils

The first synthetic lubricants were developed in the 1930s and 1940s by Hermann Zorn (the "father of synthetic lubricants") at IG Farben in Oppau and later in Leuna . The starting point was experiments with crude oil and various additives and later synthesis with ethylene . The first synthetic lubricating oil (see also synthetic oil ) of this type was the SS 906. The importance of these synthetic lubricating oils lay among other things in the development of viscosity even under extreme temperature conditions (e.g. German operations on the Eastern Front during World War II). This work led to the production of over 3500 esters in the years mentioned, including diesters and polyol esters .

Biogenic oils

There is a relatively large range of high-quality oils based on renewable raw materials for two- and four-stroke engines ( biogenic lubricants ); these usually consist of synthetic esters based on vegetable oil. By not using zinc or phosphorus-rich additives, you can also increase the durability of catalyst systems. Corresponding oils are being developed for diesel engines .

In 2003, the proportion of biogenic engine oils was only 0.02% and thus 61 t, although the oils have comparable properties. In 2005 the share was still well below 1% of the total market, but in terms of volume it had meanwhile reached 2,000 t. The reason for the low proportion is likely to be the higher price and less awareness of the biogenic oils.

Multigrade oils

With the discovery of polymers at the end of the 1960s, multigrade oils were developed. These oils have the property that they do not change their viscosity as much at different temperatures as single-grade oils. You can use the same oil in summer and winter, and starting the engine is made much easier. Even when the engine is cold, lubrication takes place faster, which reduces the wear and tear caused by cold starts. Because of these advantages, single-grade oils quickly disappeared completely from the market. The oil manufacturers' chemists also discovered that there are synthetic materials that lubricate just as well as mineral oils and have a few other beneficial properties. These properties can also be defined more precisely than with the natural product petroleum.

This was the hour of birth of synthetic oils , which now have outstanding properties. They can be produced for very large viscosity ranges, have good cold flow properties, do not tend to coke and are very pressure and temperature stable. They are pressure-resistant in two ways: On the one hand, they build up a very stable lubricating film that does not tear off even under extreme loads, and on the other hand, the structure of the molecules is more difficult to destroy during operation than with mineral oil. In some cases, only synthetic engine oils can be used for highly stressed sports engines.

Mixing different oils

Vegetable oils, for example a biodegradable chain spray based on rapeseed oil , cannot be mixed with lubricating oils or fats of fossil origin; the oils dissolve into one another, but cannot be used technically.

When mixing synthetic and mineral oils, opinions are controversial. On the one hand, it is said that today's oils can be mixed without any problems; on the other hand, the objection is that mixing reduces the effect of the additives . Motor oils that meet the API specification must always be miscible with one another; the quality must then still correspond to that of the lowest of the oils contained.

Low-viscosity oils

(Fully) synthetic low-viscosity oils enable fuel savings of 1 to 6%. Since the partially reduced HTHS viscosity (oils such as 0W-30, 0W-40, 5W-30, 5W-40) can lead to lubrication problems, approval from the motor manufacturer is required.


SAE specification

The SAE viscosity classes were in 1911 from the S ociety of A utomotive E ngineers set to give consumers the choice to facilitate the proper oil. Single grade oils have an identifier in the format “SAE xx” or “SAE xxW” (W = winter). The smaller numbers stand for thin oils, the larger ones for more viscous oils. With the introduction of multigrade oils, the system could no longer be used and was consequently expanded: The format is now "SAE xxW-yy". This notation means that at 0 ° F (approx. −18 ° C) the properties of the oil in question correspond to a single grade oil with  viscosity SAE xxW, at 210 ° F (approx. 99 ° C) it corresponds to an SAE yy oil. To achieve this property, multigrade oils contain polymers that change their spatial structure as a function of temperature. The molecules are clearly shown tangled up in cold oil. As the temperature rises, the molecules stretch more and more, thereby increasing the friction between the particles.

An inexpensive standard mineral oil usually has a viscosity of SAE 20W-40 or 15W-40. High-quality synthetic oils have now reached the viscosity ranges 0W-20, 5W-50 and 10W-60. In principle, any oil that covers the prescribed area can be used. So if a 20W-40 oil is required, the engine will run fine with a 10W-40 or 20W-50 oil without suffering any damage. However, the oil manufacturers recommend the use of special motorcycle oils for use in motorcycle engines with a common engine / gearbox oil circuit; Among other things, to avoid problems with slipping clutches (see also JASO specification). They also recommend not to use low-viscosity oils (i.e. those with SAE values ​​lower than 5W-yy) because a more viscous base oil is more stable over the long term. In particular, the extremely high pressures and shear loads that occur in the transmission break down the above-mentioned polymers (which must be contained in larger proportions in oils with a large viscosity range) over time. This is one of the reasons why the oil loses viscosity over time.

The viscosity describes only one property of an oil and does not contain any information about the quality, but is important for maintaining the correct oil pressure. Too high an oil pressure can damage seals, and too low a pressure can damage the bearings.

The SAE viscosity classes 70W to 250 are used for the classification of gear oils.

API specification

API classifications were from the A merican P etroleum I nstitute created. They define certain minimum requirements for engine oils. There are different classifications for gasoline engines and diesel engines , identified by the letter S (Service, or Spark Ignition) for gasoline engines and C (Commercial, or Compression Ignition) for diesel engines, as well as a further letter indicating the quality level. The higher the additional letter in the alphabet, the more demanding the tests on the oil. Thus, an engine oil with the API SL identifier has a higher quality class than one with API SG. The currently highest quality classes are SN and CJ.

The following is a list of some of the existing classes with a brief description:

Otto engine oils:

API class name comment
API-SA Regular engine oils possibly with pour point improvers and / or anti-foam agents (until 1930)
API SB Motor oil for low-stress Otto engines with active ingredients against aging, corrosion and wear (after 1930)
API-SC Motor oil for medium-duty Otto engines. Like SB additionally active ingredients against coking (from 1964 to 1967)
API SD Motor oil for severe operating conditions in Otto engines (from 1968 to 1971)
API-SE Motor oil for very high requirements in Otto engines (from 1971 to 1979)
API SF Motor oil for very high requirements in Otto engines such as SE, additionally improved wear protection and sludge-carrying capacity (from 1980 to 1987)
API-SG Motor oil for the highest requirements such as SF, additional protection against (black) sludge formation (from 1987 to 1993)
API-SH Motor oil for the highest requirements such as SG, additional requirements for the lubricant film breakage at high temperatures and high shear loads ( HTHS for H igh T emperature H igh S hear ) and the evaporation losses (from 1993 to 1996)
API-SJ Successor classification to API SH. Stricter requirements regarding evaporation loss (valid from October 1996).
API-SK / SL Successor classifications to API SJ (valid from 2001)
API-SM Motor oil for extremely high requirements in terms of oxidation stability, engine cleanliness, wear protection, aging behavior and performance at low temperatures. (valid from 2004)
API-SN Introduced in October 2010 for 2011, also suitable for older vehicles, designed for improved high-temperature protection on pistons, stricter sludge control, higher seal compatibility. API SN with resource improvement ILSAC GF-5 through the combination of API SN improved performance for lower fuel consumption, turbocharger protection, compatible with exhaust gas purification systems, and protection of engines that are operated with fuels containing ethanol up to E85 (valid from 2011).
API-SN Plus This specification was developed to respond to the LSPI problem with turbocharged direct injection petrol. The specification is backwards compatible with API SN, only additional tests were introduced due to the LSPI problem.

Diesel engine oils:

API class name comment
API CC Motor oils for low loads
API CD Engine oils for high loads, turbo-tested
API-CE Engine oils for the highest demands, turbo-tested
API-CF-4 Class CE engine oils with a low proportion of organometallic additives and higher requirements with regard to oil consumption and deposits on pistons.

Two-stroke oils: The classifications API TA to TC specifically designate two-stroke oil (see below: two-stroke oil classes)

Others: In addition to the API specifications, there are also the MIL specifications of the US armed forces , which are of no practical importance in Germany, as well as the specifications of the CCMC or the successor organization ACEA (Association of European Automobile Manufacturers).

ACEA specification

The motor oil specifications of the Association des Constructeurs Européens d'Automobiles are adapted to the requirements for an engine for operation according to European conditions and currently (2008) represent the current standard for motor oils. In addition to engines of European design, the standards also take into account some American models and Test runs and thus guarantee a certain degree of integration with the API classifications.

There are four categories:

A = Otto engines
B = small-volume diesel engines in cars, vans and small trucks
C = passenger car petrol and diesel engines with particle filters
E = truck diesel engines

These are further differentiated into classes A for gasoline engines and B for diesel engines:

A1 / B1: low-friction engine oils, SAE 0W-30, 5W-20, 5W-30, 10W-30; reduced HTHS viscosity (2.9-3.5 mPa × s)
A2 / B2: Standard engine oils, HTHS viscosity (> 3.5 mPa × s)
A3 / B3: Premium engine oils - particularly shear stable, SAE 0W-X, 5W-X, 10W-40, 15W-40 for extended intervals, HTHS viscosity> 3.5 mPa × s
A3 / B4: like A3 / B3 but also for DI diesel including CR diesel, SAE 0W-30, 0W-40, 5W-30, 5W-40, 10W-40; A4 reserved for DI Otto; HTHS viscosity> 3.5 mPas
A5 / B5: Premium low-viscosity oils: similar to A3 / B4, SAE 0W-30, 5W-30 but lower HTHS viscosity such as A1 / B1 (<3.5 mPa × s) for longer intervals
Classification C for passenger car diesel engines with particle filters denotes so-called low SAPS oils. These have in the combustion very limited proportions of S Ulfat a cal, P hosphor and S on chwefel (SAPS), which might adversely affect the ash-forming constituents, the permeability of the particulate filter.
C1: low-SAPS oil with reduced HTHS viscosity <2.9 mPa · s, low viscosity (0W-X, 5W-X), performance such as A5 / B5 but with very limited amounts S Ulfat a cal, P hosphor, S chwefel.
C2: Low-SAPS oil with reduced HTHS viscosity> 2.9 mPa × s, low viscosity (0W-X, 5W-X), performance like A5 / B5 with limited but higher proportions of sulfated ash , phosphorus, sulfur than for C1-04.
C3: Low-SAPS oil with high HTHS viscosity> 3.5 mPa × s, low viscosity (0W-X, 5W-X), performance like A3 / B4 with limited but higher proportions of sulphated ash, phosphorus, sulfur than for C1-04.

However, there is a trade-off between the “SAPS” ingredients in oils with high shear stability and the resulting combustion residues.

In simplified terms, it can be said that the HTHS viscosity indicates the flow strength and thus the stability of the lubricating film of an engine oil at an elevated temperature - if the value is above 3.5 mPa.s then the oil is very shear-stable even at high temperatures. Values ​​below this (below 3.5 mPa × s) are referred to as reduced HTHS viscosity, which, due to the reduced flow toughness, can mean less friction loss in the engine and thus fuel savings, but also less lubrication and shear stability.

Following the example of the C classification for passenger car diesel engines with particle filters, one can say in a nutshell: Oils according to ACEA C1 have a greatly reduced HTHS viscosity, which can help to save fuel, is one of the low SAPS oils Class best for the diesel particulate filter (DPF), because they are the least likely to cause problems, but oils according to ACEA C1 do not have as good lubrication stability as, for example, compared to the other oils (ACEA C2 / C3) of this specification. (⇒ C1 = better for DPF, C3 = better for engine)

Attention! Oils with a reduced HTHS viscosity are special oils whose use requires that the vehicle manufacturer has coordinated the entire construction chain accordingly. In the case of older or unsuitable vehicles, such oils can even lead to engine damage in extreme cases or, conversely, the diesel particulate filter can clog.

Therefore, you must pay close attention to the manufacturer's approvals.

JASO specification

Classification of the Japanese Automotive Standards Organization , a specification for simple requirements, originally mainly used in Asia. Because modern low-friction car oils are not suitable for motorcycles with oil bath clutches (the coefficient of friction of the clutch becomes so low that it slips), but a minimum coefficient of friction is not specified by the API specification, motorcycle manufacturers write a classification of the oil in addition to the API specification according to JASO-MA, -MA1 or -MA2.

Class / norm comment
JASO (T904) MA Motorcycle oil, 4-stroke engines, suitable for oil bath clutches
JASO (T904) MA1 Motorcycle oil, 4-stroke engines, suitable for oil bath clutches
JASO (T904) MA2 Motorcycle oil, 4-stroke engines, suitable for oil bath clutches
JASO (T904) MB Motorcycle oil, 4-stroke engines with dry clutch or separately lubricated gears

Two-stroke oil classes

Two-stroke oils are divided into the classes API TA to TC for mopeds , motorcycles , lawn mowers , chainsaws , etc., as well as API TD and the NNMA classes TC-W (corresponds to API TD), TC-WII or TC-W3 for two-stroke outboard motors . Here, too, the later letter or the higher number stands for the higher quality.

ISO standard / GLOBAL

GLOBAL is an association of European two-stroke engine manufacturers that writes down the performance requirements in ISO specifications.

class Operating conditions
ISO-L-EGB (Global GB) medium (= JASO FB)
ISO-L-EGC (Global GC) medium and low-smoke (= JASO FC)
ISO-L-EGD (Global GD) heavy and low-smoke (> JASO FD)
Specification according to API standard
class Operating conditions
API-TA (TSC-1) Mopeds
API-TB (TSC-2) Scooters and motorcycles
API-TC (TSC-3) High performance motors
API-TD (TSC-4) Outboard motors according to NMMA TC-WII


Specification according to JASO standard
class Operating conditions
JASO (M345) FA light
JASO (M345) FB medium
JASO (M345) FC medium + low smoke
JASO (M345) FD heavy + low smoke


NMMA specification

In fact, only one NMMA class is valid for requirements in outboard motors .

specification Operating conditions
BIA TC-W no longer valid
NMMA TC-WII no longer valid
NMMA TC-W3 highest requirements for outboard motors


Gear oils

API classification

Gear oils are described with the abbreviation GL (gear lubricant) and the numbers 1 to 6. The numbers indicate the load capacity of the oil.

The API classification differentiates between the grades for gear oils

class Applications, operating conditions
API GL-1 Oils for light applications. The oils have no additives . Occasionally, small amounts of antioxidants, corrosion inhibitors or anti- foaming agents are added. The API GL-1 classification is intended for bevel gears , worm gears and non-synchronized gearboxes in trucks or agricultural machinery.
API GL-2 Moderate oils. The oils contain wear-reducing additives and are intended for worm gears with higher loads. Recommended for the perfect lubrication of transmissions in tractors and agricultural machines.
API GL-3 Moderate oils. The oils contain up to 2.7% additives. For the lubrication of bevel gears and gearboxes on trucks. Not recommended for hypoid gears .
API GL-4 Oils for light to heavy conditions. The oils contain up to 4% wear-reducing additives. For the lubrication of bevel gears and hypoid gears with a small offset, truck gears and rear axle drives. Recommended for non-synchronized manual transmissions in US trucks, tractors and buses, for main and auxiliary transmissions of all vehicles. These oils form the minimum standard for all synchronized gearboxes, especially in Europe.
API GL-5 Oils for harsh conditions. The oils contain up to 6.5% wear-reducing additives. For the lubrication of bevel gears and hypoid gears with a large offset. As a universal oil for all differential gears except gear shift gears. Some of these oils have special manufacturer approvals, which can then only be used to lubricate the associated gear shifting gear.

API GL-5 oils can be used in limited slip differentials with friction disks (limited-slip locks), provided the oils meet the specifications according to MIL-L-2105D or ZF TE-ML-05. Typically the classification is then, for example, API GL-5 + or API GL-5 LS. Conventional oils can be made suitable for LS locks by adding a friction modifier.

API GL-6 Oils for very rough conditions (very high sliding speed on the tooth flanks and considerable shock loads). The oils contain up to 10% wear-reducing additives. However, it has been shown that GL-5 also adequately meets the specifications. Therefore the specification GL-6 has been withdrawn.



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See also

Web links

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