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'''Моторные масла''' — масла, применяемые для смазывания поршневых двигателей внутреннего сгорания.

В зависимости от назначения их подразделяют на масла для дизелей, масла для бензиновых двигателей и универсальные моторные масла, которые предназначены для смазывания двигателей обоих типов. Все современные моторные масла состоят из базовых масел и улучшающих их свойства присадок.

По температурным пределам работоспособности моторные масла подразделяют на летние, зимние и всесезонные. В качестве базовых масел используют дистиллятные компоненты различной вязкости, остаточные компоненты, смеси остаточного и дистиллятных компонентов, а также синтетические продукты (поли-альфа-олефины, алкилбензолы, эфиры). Большинство всесезонных масел получают путем загущения маловязкой основы макрополимерными присадками.

По составу базового масла моторные масла подразделяют на синтетические, минеральные и частично синтетические (смеси минерального и синтетических компонентов).

'''Motor oil''', or '''engine oil''', is a liquid used for lubrication of various internal combustion engines. While the main function is to lubricate moving parts, motor oil also cleans, inhibits corrosion, improves sealing and cools the engine by carrying heat away from the moving parts. The majority of motor oils are derived from petroleum. Motor oil mostly consists of hydrocarbons: organic compounds consisting entirely of hydrogen and carbon.
 

==Use==
Motor oil is a motor or road vehicles such as commercial vehicles, non-road vehicles such as go-karts, power by converting the energy to heat. Contact between moving surfaces also wears away those parts, which could lead to lower efficiency and degradation of the motor. This increases fuel consumption and decreases power output and can, in extreme cases, lead to total engine failure. 

Lubricating oil creates a separating film between surfaces of adjacent moving parts to minimize direct contact between them, decreasing friction, wear, and production of excessive heat, thus protecting the engine. Motor oil also carries away heat from moving parts, which is important because materials tend to become softer and less abrasion-resistant at high temperatures. Some engines have an additional oil cooler for this purpose.

In petrol (gasoline) engines, the top compression ring can expose the motor oil to temperatures of 320&nbsp;°F (160&nbsp;°C). In diesel engines the top ring can expose the oil to temperatures over 600&nbsp;°F (315&nbsp;°C). Motor oils with higher viscosity indices thin less at these higher temperatures.

Coating metal parts with oil also keeps them from being exposed to oxygen, inhibiting oxidation at elevated operating temperatures preventing rust or corrosion. Corrosion inhibitors may also be added to the motor oil. Many motor oils also have detergent and dispersant additives to help keep the engine clean and minimize oil sludge build-up.

Rubbing of metal engine parts inevitably produces some microscopic metallic particles from the wearing of the surfaces. oil filter to remove harmful particles. An oil pump, a vane or gear pump powered by the vehicle engine, pumps the oil throughout the engine, including the oil filter. Oil filters can be a ''full flow'' or ''bypass'' type.

In the bearings (main bearings and big-end bearings), and rods connecting the cylinders. This oil film also serves as a seal between the piston rings and cylinder walls to separate the combustion chamber in the cylinder head from the crankcase. The oil then drips back down into the oil pan.<ref>[http://auto.howstuffworks.com/engine.htm "How Car Engines Work"]</ref> <ref>[http://www.tpub.com/content/construction/14264/css/14264_242.htm "Types of Lubricating Systems"]</ref>.

==Other oils==
While it may still be used in ''motor vehicles'', ATF or Automatic Transmission Fluid is a separate type of specialist lubricating fluid. Varying specifications of ATF are used in automatic gearboxes and some power steering systems, and should ''not'' be used to lubricate the engine. It is typically colored dark red to distinguish it from the motor oil and other fluids in the vehicle.

Other non-motor oils include differentials oils. These are used in manual gearboxes and driven axles. They could include specialty uses including '''EP''' (Extreme Pressure), hypoid, and limited slip functions. Again, they are ''not'' to be used for engine lubrication.

==Non-vehicle oils==
Other kinds of motors also use motor oil, as well as engines that are not in vehicles such as those for snow throwers (blowers), chain saws, toy engines like those in model airplanes, certain gardening equipment like weed/grass trimmers, leaf blowers, soil cultivators, etc. Often, the applications are not exposed to as wide a temperature range in use as vehicles, so these oils may be single grade or have less viscosity index improver. 2-cycle oil is used differently than other motor oils in that it is pre-mixed with the gasoline or fuel, often in a gasoline: oil ratio of 50:1, and burned in use along with the gasoline. 

In addition to the 2-cycle oil used if they have gasoline engines, chain saws also separately use "''bar and chain oil''" for lubricating the surfaces where the cutting chain moves around bar.

Other examples of mechanical equipment often using oil include oil-driven hydraulic equipment, and turbines.

The oil properties will vary according to the individual needs of these devices.

==Properties==

Most motor oils are made from a heavier, thicker petroleum hydrocarbon base stock derived from crude oil, with additives to improve certain properties. One of the most important properties of motor oil in maintaining a lubricating film between moving parts is its viscosity. The viscosity of a liquid can be thought of as its "thickness" or a quantity of resistance to flow. The viscosity must be high enough to maintain a satisfactory lubricating film, but low enough that the oil can flow around the engine parts satisfactorily to keep them well coated under all conditions. The viscosity index is a measure of how much the oil's viscosity changes as temperature changes. A higher viscosity index indicates the viscosity changes less with temperature than a lower viscosity index.

Motor oil must be able to flow at cold winter temperatures to lubricate internal moving parts upon starting up the engine. Another important property of motor oil is its ''pour point'', which is indicative of the lowest temperature at which the oil could still be poured satisfactorily. The lower the pour point temperature of the oil, the more desirable the oil is when starting up at cold temperature. 

Oil is largely composed of hydrocarbons which can burn if ignited. Still another important property of motor oil is its petroleum refinery, fractional distillation separates a motor oil fraction from other crude oil fractions, removing the volatile components which ignite more easily, and therefore increasing the oil's flash point.

Another test done on oil is to determine the Total Base Number (TBN), which is a measurement of the reserve alkalinity of an oil to neutralize acids. The resulting quantity is determined as mg KOH/ (gram of lubricant). Analogously, Total Acid Number (TAN) is the measure of a lubricant's acidity. Other tests include zinc, phosphorus, or sulfur content, and testing for excessive foaming. 

Different motor oils are sold for Diesel fuel engines, with many claimed to contain a higher level of detergents and dispersants to keep fine combustion soot in suspension. However, for some brands only the packaging varies (the oil is the same), and in general a diesel engine can use any good quality oil of the correct grade and specification.

The NOACK volatility (ASTM D-5800) Test determines the evaporation loss of lubricants in high temperature service. A maximum of 15 percent evaporation loss is allowable to meet API SL and ILSAC GF-3 specifications.

==Grades==
thumb|right|225px|Range of Motor Oils on display in Kuwait

The kinematic viscosity. SAE viscosity gradings 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 viscocity, at lower temperature.  <bR>
Viscocity 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 viscocity, and thus higher SAE code.

Note that the 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 (eg 75W-140) do not mean that it is necessarily higher viscosity than an engine oil.

===Single-grade===
For single-grade oils, the kinematic viscosity is measured at a reference temperature of 100°C (212°F) in units of mm²/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.  These numbers are often referred to as the weight of a motor oil.  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 unimproved with additives changes considerably with temperature.  As the temperature increases, the viscosity of the oil decreases logarithmically in a relatively predictable manner.  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.  A single-grade oil graded at the hot temperature is expected to test into the corresponding grade at the winter temperature; i.e. a 10 grade oil should correspond to a 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===
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 a low viscosity at the engine's 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 VIs 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 a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened. This slope representing the change with temperature depends on the nature and amount of the additives to the 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''' (again 'W' is for Winter, not Weight) 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 can be pumped. "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 real-world ability of an oil to crank in the cold is diminished soon after put into service. The motor oil grade and viscosity to be used in a given vehicle is specified by the manufacturer of the vehicle (although some modern European cars now make no viscosity requirement), but can vary from country to country when climatic or mpg constraints come into play. Oil circulates through the piston oil rings to cool and lubricate the compression rings. Inside gasoline engines, the top compression ring is exposed to temperatures as high as 320 °F (160 °C). 

Many new vehicles are marked to use 5W-20 oil (Honda, Ford, and more recently Toyota) which is not much thinner than a 30W oil. Nay-sayers of 20W oil's ability to protect engines should note that typically, 30W oils shear down into the 20W range anyway. Most engine wear is during start-up and warm-up period, where the thinner 20W oil's flow is desirable. Overall, lab test results of the wear metals contained in used oil samples show low or lower wear with 20W than 30 in applications it is specified for. Some ultra fuel efficient and hybrid vehicles are marked to use 0W-20 oil. For some selective mechanical problems with engines, using a more viscous oil can ameliorate the symptoms, i.e. changing from 5W-20 to 20W-50 may eliminate a knocking noise from the engine but doesn't solve the problem, just "masks" it. Excess amounts of oil consumed by an engine burning it can be addressed by using a thicker oil, a 10W-40 might not burn off as fast compared to a 5W-30. A newer product that also addresses this issue is the "High-Miles" oils now marketed. They tend to be slightly thick for their grades, contain extra additives and seal conditioners. Apparently the formulation of these oils works well in many instances.

===Turbine===
Turbine motor oils are designed somewhat differently than reciprocating engine oils traditionally used in automobiles. Deposit control and corrosion are not significant issues when formulating a turbine oil, and the shear stresses that turbine oils are exposed to are minimal in light of the fact that turbines are naturally balanced rotating machines unlike reciprocating engines. Turbine oils tend to have the ISO VG range 32, 46, and 68 (cSt at 40°C), and make extensive use of polyolester, polyalphaolefin, and Group II as base stock due to the high temperatures they must endure. Varnish is the most problematic contaminant, which can only be detected accurately with the ultra centrifuge test resulting in the "UC value".

In most aviation compressors into the regions of the engine with lubricated bearings and gearboxes. The gas flow associated with running the turbine provides significant convective cooling that disappears when the engine is shut down, leaving residual heat that causes temperatures within the turbine to rise dramatically, an often-misunderstood phenomenon.

==Standards==
===American Petroleum Institute===
The inhibit fractionally distilled fractionally distilled hydrocracked to further refine and purify it. Group III base stocks have similar characteristics to Group II base stocks, except that Group III base stocks have higher viscosity indexes. Group III base stocks are produced by further hydrocracking of Group II base stocks, or of hydroisomerized slack wax, (a byproduct of the dewaxing process). Group IV base stock are polyalphaolefins (PAOs). Group V is a catch-all group for any base stock not described by Groups I to IV. Examples of group V base stocks include polyol esters, polyalkylene glycols (PAG oils), and perfluoropolyalkylethers (PFPAEs). Groups I and II are commonly referred to as mineral oils, group III is typically referred to as synthetic (except in Germany and Japan, where they must not be called synthetic) and group IV is a synthetic oil. Group V base oils are so diverse that there is no catch-all description.

=====API Service Classes=====
The API service classes<ref>[http://new.api.org/certifications/engineoil/categories/upload/ShelfCard_English.pdf API Service Guide]</ref> have two general classifications: '''S''' for "Service" (orgininating from Spark ignition) (typical passenger cars and light trucks using gasoline engines), and '''C''' for "Commercial" (originating from Compression ignition) (typical diesel equipment).

Note that the API oil classification structure has eliminated specific support for wet-clutch motorcycle applications in their descriptors, and API SJ and newer oils are referred to be specific to automobile and light truck use.  Accordingly, motorcycle oils are subject to their own unique standards.

The latest API service standard designation is SM for gasoline automobile and light-truck engines.  The SM standard refers to a group of laboratory and engine tests, including the latest series for control of high-temperature deposits.  Current API service categories include SM, SL and SJ for gasoline engines.  All previous service designations are obsolete, although motorcycle oils commonly still use the SF/SG standard.  The obsolete SH standard was the last standard to contain the integral zinc and phosphorus (ZDDP) levels needed for proper lubrication of approx. pre-1990 cars.  Oils with higher ZDDP levels are still available from some manufactures, although much information is proprietary.