Motor oil

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A typical container of motor oil, with some in a glass.

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.

[edit] Use

Motor oil is a lubricant used in internal combustion engines. These include motor or road vehicles such as cars and motorcycles, heavier vehicles such as buses and commercial vehicles, non-road vehicles such as go-karts, snowmobiles, boats (fixed engine installations and outboards), ride-on lawn mowers, large agricultural and construction equipment, trains and aircraft, and static engines such as electrical generators. In engines there are parts which move very closely against each other causing friction which wastes otherwise useful 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 °F (160 °C). In diesel engines the top ring can expose the oil to temperatures over 600 °F (315 °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. Sludge also accumulates in the engine. Such particles could circulate in the oil and grind against the moving parts, causing erosion and wear. Because particles inevitably build up in the oil, it is typically circulated through an 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 crankcase of a vehicle engine, motor oil lubricates rotating or sliding surfaces between the crankshaft journals bearings (main bearings and big-end bearings), and rods connecting the pistons to the crankshaft. The oil collects in an oil pan, or sump at the bottom of the crankcase. In some small engines such as lawn mower engines, dippers on the bottoms of connecting rods dip into the oil at the bottom and splash it around the crankcase as needed to lubricate parts inside. In modern vehicle engines, the oil pump takes oil from the oil pan and sends it through the oil filter into oil galleries, from which the oil lubricates the main bearings holding the crankshaft up at the main journals and camshaft bearings operating the valves. In typical modern vehicles, oil pressure-fed from the oil galleries to the main bearings enters holes in the main journals of the crankshaft. From these holes in the main journals, the oil moves through passageways inside the crankshaft to exit holes in the rod journals to lubricate the rod bearings and connecting rods. Some simpler designs relied on these rapidly moving parts to splash and lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. However, in modern designs, there are also passageways through the rods which carry oil from the rod bearings to the rod-piston connections and lubricate the contacting surfaces between the piston rings and interior surfaces of 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. To see these details on a crankshaft, see "How Car Engines Work" at HowStuffWorks or "Types of Lubricating Systems" at Integrated Publishing.

[edit] 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 gear or transmission, and differentials oils. These are used in manual gearboxes and driven axles. They could include speciality uses including EP (Extreme Pressure), hypoid, and limited slip functions. Again, they are not to be used for engine lubrication.

[edit] Non-vehicle oils

Other kinds of motors also use motor oil, as well as engines that are not in vehicles such as those for electrical generators. Examples include 4-stroke or 4-cycle internal combustion engines such as those used in many "walk behind" lawn mowers and other engines, and special 2-stroke oil used in 2-stroke or 2-cycle internal combustion engines such as those used in various smaller engines like 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 compressors, vacuum pumps, diffusion pumps, sewing machines and other devices with motors, oil-driven hydraulic equipment, and turbines.

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

[edit] Properties

Spills of engine oil onto wet concrete create characteristic iridescent (rainbow-hued) stains — a thin layer of oil floats above the water.

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 flash point, the lowest temperature at which the oil gives off vapors which can ignite. It is dangerous for the oil in a motor to ignite and burn, so a high flash point is desirable. At a 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.

[edit] Grades

Range of Motor Oils on display in Kuwait

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 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.
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.

[edit] 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.

[edit] 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 30 weight oil. Nay-sayers of 20 weight oil's ability to protect engines should note that typically, 30 weight oils shear down into the 20 weight range anyway. Most engine wear is during start-up and warm-up period, where the thinner 20 weight oil's flow is desirable. Overall, lab test results of the wear metals contained in used oil samples show low or lower wear with 20 weight 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.

[edit] 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 gas turbine applications, peak lubricant temperatures are not reached during engine operation, but after shutdown, when heat has been able to migrate from the combustor cans and the 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.

[edit] Standards

[edit] American Petroleum Institute

The American Petroleum Institute (API) sets minimum performance standards for lubricants. Motor oil is used for the lubrication, cooling, and cleaning of internal combustion engines. Motor oil may be composed of a lubricant base stock only in the case of non-detergent oil, or a lubricant base stock plus additives to improve the oil's detergency, extreme pressure performance, and ability to inhibit corrosion of engine parts. Lubricant base stocks are categorized into five groups by the API. Group I base stocks are composed of fractionally distilled petroleum which is further refined with solvent extraction processes to improve certain properties such as oxidation resistance and to remove wax. Group II base stocks are composed of fractionally distilled petroleum that has been 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.

[edit] API Service Classes

The API service classes^[1] 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^{[citation needed]}. Oils with higher ZDDP levels are still available from some manufactures, although much information is proprietary.

There are seven diesel engine service designations which are current: CJ-4, CI-4 Plus, CI-4, CH-4, CG-4, CF-2, and CF. All others are obsolete.

It is possible for an oil to conform to both the gasoline and diesel standards. Engine oil which has been tested and meets the API standards may display the API starburst symbol with the service designation on containers sold to oil users. The latest guide to API oil certifications can be found at API EngineOilGuide2006 (PDF).

[edit] ILSAC

The International Lubricant Standardization and Approval Committee (ILSAC) also has standards for motor oil. Their latest standard, GF-4^[2] was approved in 2004. A key test is the Sequence IIIG [1] , 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.

The IIIG test is about 50% more difficult [2] than the previous IIIF test, used in GF-3 and API SL oils. Engine oils bearing the API starburst symbol since 2005 are ILSAC GF-4 compliant. [3]

[edit] ACEA

The ACEA (Association des Constructeurs Européens d'Automobiles) performance/quality classifications A3/A5 tests used in Europe are even tougher than the API and ILSAC standards. In cars of American origin, it is debatable whether this matters for normal drain intervals (5,000-7,000 miles). However, most modern cars of European origin frequently specifically refer oils meeting ACEA standards, and many European cars now make no reference to API specifications. CEC (The Co-ordinating European Council) is the development body for fuel and lubricant testing in Europe and beyond, setting the standards via their European Industry groups; ACEA, ATIEL, ATC and CONCAWE.

[edit] 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.

[edit] 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 hydrocracking 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 Longlife standards, Porsche, and the PSA Group of Peugeot and Citroën.

In recent times, very highly specialised "extended drain" "longlife" oils have arisen, whereby, taking Volkswagen Group vehicles, a petrol engine can now go up to 2 years or 30,000 km (a little under 20,000 miles), and a diesel engine can go up to 2 years or 50,000 km (a little under 30,000 miles) - before requiring an oil change. BMW, GM, Mercedes and PSA all have their own similar longlife oil standards.

Furthermore, virtually all European OEM standards require a long duration of longevity of the HTHS (High Temperature, High Shear) viscosity, many around the 3.5 cP.

As a result of this ultra-modern 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, nor 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 ½ a litre of non-OEM oil.

[edit] Other 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 buildup, 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.

There are other additives available commercially which can be added to the oil by the user for purported additional benefit. Some of these 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.

In the 1980s and 1990s, additives with suspended PTFE particles were available to consumers to increase motor oil's ability to coat and protect metal surfaces. There is controversy as to the actual effectiveness of these products as they can solidify and clog the oil filters.

Some molybdenum disulfide containing additives to lubricating oils are claimed to reduce friction, bond to metal, or have anti-wear properties.

Various other extreme-pressure additives and antiwear additives

[edit] Synthetic oil and synthetic blends

Synthetic lubricants were first synthesized, or man-made, in significant quantities as replacements for mineral lubricants (and fuels) by German scientists in the late 1930s and early 1940s because of their lack of sufficient quantities of crude for their (primarily military) needs. A significant factor in its gain in popularity was the ability of synthetic-based lubricants to remain fluid in the sub-zero temperatures of the Eastern front in wintertime, temperatures which caused petroleum-based lubricants to solidify due to their higher wax content. The use of synthetic lubricants widened through the 1950s and 1960s due to a property at the other end of the temperature spectrum, the ability to lubricate aviation engines at temperatures that caused mineral-based lubricants to break down. In the mid 1970s, synthetic motor oils were formulated and commercially applied for the first time in automotive applications. The same SAE system for designating motor oil viscosity also applies to synthetic oils.

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 as well as "others" like GTL (Methane Gas-to-Liquid) (Group V) and polyalpha-olefins (Group IV), although actual base oil content of finished blended motor oils is not a factor. 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.

Synthetic lubricants are designed for "long life" extended drain intervals, but most users rarely run them long enough to gain a cost-effective return. If a "synthetic" oil costs 2 to 3 times as much as a conventional oil, it would have to be used for 2 to 3 times longer than a conventional oil just to break even.

[edit] Maintenance

In engines, there is inevitably some exposure of the oil to products of internal combustion, and microscopic coke particles from black soot accumulate in the oil during operation. Also the rubbing of metal engine parts inevitably produces some microscopic metallic particles from the wearing of the surfaces. Such particles could circulate in the oil and grind against the part surfaces causing wear. The oil filter removes many of the particles and sludge, but eventually the oil filter can become clogged, if used for extremely long periods. Experienced mechanics will cut open the filter canisters to inspect for degree of loading. The motor oil and especially the additives also undergo thermal and mechanical degradation. For these reasons, the oil and the oil filter need to be periodically replaced.

The vehicle manufacturer may specify which SAE viscosity grade of oil should be used for the vehicles it produces, but many different weights can actually be used. Some manufacturers have specific quality test requirements or "specs" for service in their particular make. In the USA, quick oil change shops recommended intervals of 3,000 miles or every 3 months, but one oil brand now markets miles-specific line with 5,000, 7,500 and even 15,000 miles performance guarantee.Mobil (2008). Mobil Clean Oils. W. M. Retrieved on 1/22, 2008.

With a degree of ambiguity about how many miles motor oil is actually good for, some people opt for a more convenient time-based schedule. Seasonal changes are desirable where the viscosity can be adjusted for the ambient temperature change, thicker for summer heat and thinner for the winter cold. As a general rule, the thinnest oil is used that does not produce excess wear. Time-based intervals account for both the short trip driver who does fewer miles, but builds up more contaminates, as well as the long highway trips that are much easier on the oil. Many modern cars now list somewhat higher intervals for changing of oil and filter, with the constraint of "severe" service requiring more frequent changes with less-than ideal driving. Most commonly this applies to short trips of under 10 miles, where the oil does not get to full operating temps long enough to burn off condensation, excess fuel, and other contamination that leads to "sludge", "varnish", "acids", or other deposits. Many manufacturers have engine computer calculations to estimate the oil's condition based on the factors which degrade it such as RPMs, temperatures, and trip length; and one system adds an optical sensor for determining the clarity of the oil in the engine. These systems are commonly known as Oil Life Monitors or OLMs. Over the years, manufacturers have been able to reduce the viscosity of oil needed to correctly lubricate the engine and extend the duration of the servicable life. On the 1970s typical cars took heavy 10w-40 oil and was used for a duration of 2000 miles or less. In the 1980s 5w-30 oils were introduced to improve gas mileage and improve engine performance. A modern typical application would be Honda Motor's use of 5w-20 oil viscosity for 7500 miles without excess wear or deposits while offering the maximum mpg. Most other manufacturers use 20 weight oils as well. The latest API "SM" spec offers a substantially better product than preceding specifications.

[edit] Future

A process to break down polyethylene, a common plastic product found in many consumer containers, is used to make wax with the correct molecular properties for conversion into a lubricant, bypassing the expensive Fischer-Tropsch process. The plastic is melted then pumped into a furnace. The heat of the furnace breaks down the molecular chains of polyethylene into wax. Finally, the wax is subjected to a catalytic process that alters the wax's molecular structure leaving a clear oil. (Miller, et al., 2005)

New Biodegradable Auto Oil is making an appearance on the market. This oil is formed from fats of cattle. The benefit of this new form of motor oil is the ability to transform the oil back into soil with less negative consequences. Typical motor oil needs to go through special treatment facilities whereas biodegradable motor oil has less impact on the environment if you spill it on the ground. All used motor oils can contain toxic heavy metals, however, and even biodegradable oils should be recycled properly.

[edit] Some popular major producers

[edit] References

[edit] External links

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