Grades of motor oil Options

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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, 60 or 70. Some of the numbers can be suffixed with the letter W.


Single-grade, or monograde motor oil
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, 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 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 motor oil
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 API/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". "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 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 -30°F, a 5W at -25°F and a 10W is tested at -20°F. 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 500°F.

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.


Turbine motor oil
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.

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Gear oil is a motor oil made specifically for transmissions, transfer cases, and differentials in automobiles, trucks, and other machinery. It is of a higher viscosity to better protect the gears and usually is associated with a strong sulfur smell. The high viscosity ensures transfer of lubricant throughout the gear train. This is necessary since the devices needing this heavy oil do not have pumps for transferring the oil with only a portion of the lowermost gears bathed in an oil sump. This heavy oil can create viscous drag leading to inefficiencies in vehicle operation. Some modern automatic transaxles (integrated transmission and differential) do not use a heavy oil at all but lubricate with the lower viscosity hydraulic fluid, which is available at pressure within the automatic transmission.

Most lubricants for manual gearboxes and differentials are hypoid gear oils. These contain extreme pressure (EP) additives and antiwear additives to cope with the sliding action of hypoid bevel gears.

Gear oils are classified by the American Petroleum Institute using GL ratings. For example, most modern gearboxes require a GL4 oil, and separate differentials (where fitted) require a GL5 oil. It is important that purchasers check the oil against the vehicle manufacturer's specification to ensure it does not contain any aggressive chemicals that may attack gear components, such as the phosphor bronze used in many Japanese boxes.

API viscosity ratings for gear oils are not directly comparable with those for motor oil, and they are thinner than the figures suggest. For example, many modern gearboxes use a 75W90 gear oil, which is actually of equivalent viscosity to a 10W40 motor oil. Multigrade gear oils are becoming more common; while gear oil does not reach the temperatures of motor oil, it does warm up appreciably as the car is driven, due mostly to shear friction (with a small amount of heat conduction through the bellhousing from the engine block).

Fully synthetic gear oils are also used in many vehicles, and have a greater resistance to shear breakdown than mineral oils. They can improve the shifting performance of "difficult" gearboxes, where the excessive slipperiness of some mineral oils can impede synchromesh action.

Retrieved from "http://en.wikipedia.org/wiki/Gear_oil"

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Классификация масел по SAE

Основанная в 1911 году SAE (Society of Automotive Engineers - Общество автомобильных инженеров) была первой организацией создавшей систему классификации масел по вязкости.

Норма SAE J 300 определяет степень вязкости для каждого смазочного материала.
SAE J-300 содержит 6 зимних классов и 5 летних классов моторных масел.
Классы вязкости SAE OW, 5W, 10W, 15W, 20W, 25W относятся к зимним, а SAE 20, 30, 40, 50, 60 - к летним.

Например, S.A.E. 40 (летняя степень вязкости). Чем больше число, тем в большей степени масло будет сохранять свою вязкость при нагревании. В условиях городского движения и при спортивном вождении, а также когда высока температура воздуха, двигатель подвергается воздействию высоких температур. Важно пользоваться маслом, которое при высокой температуре в большой степени сохраняет свою вязкость для защиты двигателя.

Когда двигатель холодный, наоборот, масло обладает тенденцией сгущаться. В этом случае важно, чтобы оно оставалось жидким даже при низких температурах, чтобы протекать через двигатель, защищать его детали и способствовать пуску. Холодная вязкость обозначается в нормах S.A.E. "зимней степенью вязкости".

Например, S.A.E.10W. Число обозначает степень зимней вязкости, после этого числа всегда стоит буква "W" ("winter", то есть "зима"). Чем меньше число, тем в большей степени масло будет сохранять свою текучесть в холодную погоду или при пуске двигателя.

Моносезонные масла обычно применяются, когда рабочие температуры отличаются не намного (или для выполнения специальных задач).

Всесезонные масла обозначаются одновременно и зимней и летней степенью вязкости.
Например, S.A.E. 10W 40
где: 10W = зимняя степень вязкости
40 = летняя степень вязкости
Всесезонное масло менее подвержено воздействию температур.