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Join Date: Oct 2009
Posts: 88
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Re: Castrol vs. Mobil 1
uite aici mai multe !!!!
Grades
Range of motor oils on display in KuwaitThe Society of Automotive Engineers (SAE) has established a numerical code system for grading motor oils according to their viscosity characteristics. SAE viscosity gradings include the following, from low to high viscosity: 0, 5, 10, 15, 20, 25, 30, 40, 50 or 60. The numbers 0, 5, 10, 15 and 25 are suffixed with the letter W, designating their "winter" (not "weight") or cold-start viscosity, at lower temperature. The number 20 comes with or without a W, depending on whether it is being used to denote a cold or hot viscosity grade. The document SAE J300 defines the viscometrics related to these grades.
Kinematic viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice, at standard temperatures. The longer it takes, the higher the viscosity and thus higher SAE code.
Note that the SAE has a separate viscosity rating system for gear, axle, and manual transmission oils, SAE J306, which should not be confused with engine oil viscosity. The higher numbers of a gear oil (eg 75W-140) do not mean that it has higher viscosity than an engine oil.
[edit] Single-grade
A single-grade engine oil, as defined by SAE J300, cannot use a polymeric Viscosity Index Improver (also referred to as Vicosity Modifier) additive. SAE J300 has established eleven viscosity grades, of which six are considered Winter-grades and given a W designation. The 11 viscosity grades are 0W, 5W, 10W, 15W, 20W, 25W, 20, 30, 40, 50, and 60. These numbers are often referred to as the 'weight' of a motor oil.
For single winter grade oils, the dynamic viscosity is measured at different cold temperatures, specified in J300 depending on the viscosity grade, in units of mPa·s or the equivalent older non-SI units, centipoise (abbreviated cP), using two different test methods. They are the Cold Cranking Simulator (ASTM D5293) and the Mini-Rotary Viscometer (ASTM D4684). Based on the coldest temperature the oil passes at, that oil is graded as SAE viscosity grade 0W, 5W, 10W, 15W, 20W, or 25W. The lower the viscosity grade, the lower the temperature the oil can pass. For example, if an oil passes at the specifications for 10W and 5W, but fails for 0W, then that oil must be labeled as an SAE 5W. That oil cannot be labeled as either 0W or 10W.
For single non-winter grade oils, the kinematic viscosity is measured at a 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 SAE viscosity grade 20, 30, 40, 50, or 60. In addition, for SAE grades 20, 30, and 40, a minimum viscosity measured at 150 °C (302 °F) and at a high-shear rate is also required. The higher the viscosity, the higher the SAE viscosity grade is.
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, industrial applications, 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 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 lower viscosity at the engine's operating temperature. The difference in viscosities for most 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 VIIs are added to the oil. These additives are used to make the oil a multi-grade motor oil, however it is possible to have a multi-grade oil without the use of VIIs. The idea is to cause the multi-grade oil to have the viscosity of the base grade when cold and the viscosity of the second grade when hot. This enables one type of oil to be generally used all year. In fact, 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 viscosity grades; for example, 10W-30 designates a common multi-grade oil. The two numbers used are individually defined by SAE J300 for single-grade oils. Therefore, an oil labeled as 10W-30 must pass the SAE J300 viscosity grade requirement for both 10W and 30, and all limitations placed on the viscosity grades (for example, a 10W-30 oil must fail the J300 requirements at 5W). Also, if an oil does not contain any VIIs, and can pass as a multi-grade, that oil can be labeled with either of the two SAE viscosity grades. For example, a very simple multi-grade oil that can be easily made with modern baseoils without any VII is a 20W-20. This oil can be labeled as 20W-20, 20W, or 20. Note, if any VIIs are used however, then that oil cannot be labeled as a single grade.
The real-world ability of an oil to crank or pump when cold is potentially diminished soon after it is 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 have no viscosity requirement), but can vary from country to country when climatic or fuel efficiency constraints come into play.
OEM standards divergence
By the early 1990s, many of the European original equipment manufacturer (OEM) car manufacturers felt that the direction of the American API oil standards was not compatible with the needs of a motor oil to be used in their motors. 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. General Motors also has the 4718M standard that is used for the Chevrolet Corvette, a standard that is used in North America for selected North American performance engines, with a "Use Mobil 1 only" sticker usually placed on those cars.[citation needed]
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 (~18,600 mi), and a diesel engine can go up to 2 years or 50,000 km (~31,000 mi) - before requiring an oil change. Volkswagen (504.00), BMW, GM, Mercedes and PSA all have their own similar longlife oil standards.[citation needed] Another trend of today represent midSAP (sulfated ash <0,8 wt.-%) and lowSAP (sulfated ash <0,5 wt.-%) engine oil (see specifications: Renault RN 0720, FORD WSS-M2C934-A). The ACEA specifications C1 to C4 reflect the midSAP and lowSAP needs of automotive OEMs. Furthermore, virtually all European OEM standards require a long drains of 30.000 km and up by using HTHS (High Temperature, High Shear) viscosity, many around the 3.5 cP (3.5 mPa·s). In Japan, the HTHS figures are low as >2.6 mPas.
Because of the real or perceived need for motor oils with unique qualities, many modern European cars will demand a specific OEM-only oil standard. As a result, they may 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.
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Last edited by gtigabi; 13-12-09 at 13:06.
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Re: Castrol vs. Mobil 1
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