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Motor oil is a lubricant in various types of internal combustion engines. These include motor vehicles or Road Vehicles - the typical light automobiles (including cars, SUVs, minivans, pick-up trucks). Heavy automobiles would include Busses, Trucks and HGVs. Other vehicles, include motorcycles and mopeds, quad-bikes or ATVs, go-karts, snowmobiles, boats (fixed engine installations and outboards), ride-on lawn mowers, large agricultural and construction equipment, trains and airplanes. In engines there are parts which move very closely against each other at high speeds, often for prolonged periods of time. Such motion causes friction, absorbing otherwise useful power produced by the motor and converting the energy to useless heat. Friction also wears away the contacting surfaces of those parts, which could lead to lower efficiency and degradation of the motor. This increases fuel consumption.
Lubricating oil makes a separating film between surfaces of parts moving next to each other so as 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.
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 the higher viscosity indexes tend to thin less at these higher temperatures.
Coating metal parts with oil also keeps them from being exposed to oxygen, which inhibits their oxidation at elevated operating temperatures (basically preventing them from rusting) Corrosion inhibitors may also be added to the motor oil. Many motor oils also have detergent additives to help keep the engine clean and minimize oil sludge buildup.
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.
A typical container of motor oil, with some in a glass.Motor oil is a type of liquid oil used for lubrication by various types of internal combustion engines. While the main function is to lubricate moving parts, motor oil also cleans, inhibits corrosion, and cools the engine by carrying heat away from the moving parts. The majority of motor oils are derived from petroleum.Synthetic motor oil, consisting of artificiallysynthesized compounds, currently has a majorityshare in the motor oil market place because, while more expensive, it offers enhanced performance.Semisynthetic motor oil was introduced in 1966.Motor oil is a lubricant in internal combustion engines, typically found in automobiles and other vehicles, boats, lawn mowers, trains, airplanes.
In engines there are parts which move very closely against each other at high speeds, often for prolonged periods of time. Such motion causes friction, absorbing otherwise useful power produced by the motor and converting the energy to useless heat. Friction also wears away the contacting surfaces of those parts, which could lead to lower efficiency and degradation of the motor. This increases fuel consumption.Lubricating oil makes a film between surfaces of parts moving next to each other so as 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 abrasionresistant at high temperatures. Some engines have an additional oil cooler.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 the higher viscosity indexes tend to thin less at these higher temperatures.
Coating metal parts with oil also keeps them from being exposed to oxygen, which inhibits their oxidation at elevated operating temperatures basically preventing them from rusting Corrosion inhibitors may also be added to the motor oil. Many motor oils also have detergent additives to help keep the engine clean and minimize oil sludge buildup.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 gear pump powered by the vehicle engine, pumps the oil through 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, and rods connecting the pistons to the crankshaft. The oil collects in an oil pan 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 pressurefed 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 rodpiston 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.Automatic transmission fluid is a separate fluid. It is typically colored red to distinguish it from the motor oil and other fluids in the vehicle. oil lubricates the joints and keeps them from overheating and gasoline burns in the engine generating exhaust and powering then car.
Other kinds of motors, such as internal combustion engines in motorcycles, mopeds, outboard motors for boats, snowmobile, ATVs, personal watercraft, scooters, and gocarts, etc., also use motor oil, as well as engines that are not in vehicles such as those for electrical generators. Examples include 4stroke or 4cycle internal combustion engines such as those used in many lawn mowers and other engines, and special 2cycle oil used in 2stroke or 2cycle 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. 2cycle oil is used differently than other motor oils in that it is premixed 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 2cycle 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 oildriven compressors, vacuum pumps, diffusion pumps, sewing machines and other devices with motors, oildriven hydraulic equipment, turbines, and mechanisms using gears such as gear differentials for rear wheeldrive vehicles. The oil properties will vary according to the needs of these devices.
Most motor oils are made from a heavier, thicker petroleum hydrocarbon base stock derived from crude oil, with additives added as needed to improve the properties. One of the most important properties of motor oil in maintaining a lubricating film between moving parts is its viscosity. In layman's terms, 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 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.
The Society of Automotive Engineers, usually abbreviated as SAE, has established a numerical code system for grading motor oils according to their kinematic viscosity. For singlegrade oils, the kinematic viscosity is measured at a reference temperature of 100 °C 212 °F in units of mm²/s or the equivalent older nonSI 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, 60 or 70. 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 singlegrade 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 singlegrade 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 singlegrade 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, singlegrade motor oil is satisfactory for example, lawn mower engines.
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 singlegrade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers are added to the oil. These additives make the oil a multigrade motor oil.
The idea is to cause the multigrade oil to have the viscosity of the base number when cold and the viscosity of second number when hot. The viscosity of a multigrade 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 API/SAE designation for multigrade oils includes two grade numbers for example, 10W30 designates a common multigrade 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 singlegrade SAE 10 oil can be pumped. 5W can be pumped at a lower temperature than 10W. 0W can be pumped at a lower temperature than 5W, and thins less at temperatures above 99 °C 210 °F. The second number, 30, means that the viscosity of this multigrade oil at 100 °C 212 °F operating temperature corresponds to the viscosity of a singlegrade 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 30f, a 5w at 25f and a 10w is tested at 20f.
The realworld 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, but can vary from country to country when climatic or mpg constraints come into play.Many new vehicles are marked to use 5W20 oil Honda, Ford, and more recently Toyota which is not much thinner than a 30 weight oil. Naysayers 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 startup and warmup 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.
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 oftenmisunderstood phenomenon.
Motor oil used for vehicle engines is commonly called engine oil in American Petroleum Institute API documentation. Engine 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 nondetergent 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 other synthetic and mineral base stocks. 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 catchall description.
