Q. What is a modern lubricant ?
Ans. A lubricant is the material that lies between two surfaces that are moving with respect to each other. The presence of a lubricant affects the friction between the two surfaces. It is usually used to reduce friction, thereby reducing heat and wear, but it is also often used to cool, clean and protect the surfaces from corrosive chemical attack. A lubricant can be liquid, solid or even a gas. Greases are liquids that have been thickened by the addition of chemical or solid materials. Teflon and graphite are examples of solid lubricants.
Q. What is viscosity ?
Ans. Viscosity is a measure of a fluid's resistance to flow. For lubricating oil in general, viscosity is the most important physical property. It is viscosity, as well as the pressure and speed of movement, which determines the thickness of an oil film between two moving surfaces. This in turn determines the ability of the oil film to keep the two surfaces apart, the rate heat is generated by friction and the rate the oil flows between the surfaces and thus conveys the heat away. The oil should have a viscosity at the operating temperature that is correct for maintaining a fluid film between the bearing surfaces, despite the pressure tending to squeeze it out. While a reasonable factor of safety is usually desirable, excessive viscosity should be avoided because this can create more drag and therefore unnecessary heat generation. Viscosity is also useful for identification of grades of oil and for following the performance of oils in service. An increase in the oil's viscosity during use usually indicates that the oil has deteriorated to some extent, a decrease normally indicates dilution with fuel. The permissible extent of viscosity increase before corrective measures are taken is largely a matter of experience and judgment of the operator.
Q. What does SAE stand for ?
Ans. SAE stands for the Society of Automotive Engineers, based in the USA. The SAE grade specifies the most important parameter for engine oil mainly its viscosity. In other words it tells you the "thickness" of the oil. The lower the number, the "thinner " the oil; thus SAE 30 is less viscous than SAE 40.
Q. What is a multi-grade oil ?
Ans. These are oils designed to give better viscosities at both high and low temperatures than regular mono-grade oils. The viscosity of all oils falls as they get hot – and multi-grade oils are formulated to minimize this effect. Multi-grade oils are defined by a viscosity rating at a low temperature, as well as one at 100 C
Q. We have come across an oil having a 20W-40 rating. What does 'W' stand for ?
Ans. This is the common terminology used to indicate a multi-grade oil. 'W' signifies the winter rating of the oil, showing that it will perform well in cold weather. The lower the number prefixing the 'W', the lower the temperature the oil can withstand. Thus 10W- indicates a lower viscosity at low temperature than 20W-. The second figure shows the viscosity at 100 C, which is close to the bulk oil temperature in most water-cooled engines.
Q. What does the specification API stand for ?
Ans. API stands for the American Petroleum Institute. This body has specified the performance standards that oils used in road vehicles should meet, notably for cars and trucks made in the USA. For oils destined for use in passenger car engines, the letters API are followed by a set of two letters such as SJ, etc. This indicates the Service Level for passenger car oils. These specified performance levels have evolved through the years, from API SA to SM, in response to the changes in passenger car engine technology that, in turn, has imposed ever more severe operating conditions on the oil to achieve satisfactory lubrication.The highest API for passenger car motor oils today is API-SM.Similarly, the API designates the performance of diesel engine oils with a letter sequence such as API CF or API CH-4, and for automotive gear oils they use API GL-4.The highest API for commercial engine oils (diesel oils) today is API CI-4 Plus.Many other specifications are used to denote lubricant performance: notably the ACEA (European), JASO (Japan) and the US Military classifications.
Q. How do I choose the right oil for my vehicle ?
Ans. You should always consult the car or vehicle manual, issued by the original manufacturer. There you will find the most suitable viscosity grade and performance level. In some cases oils will be mentioned by name. Then, check the oil pack label to make sure you have the right viscosity grade and that it at least meets the performance level. Note that for many older vehicles the performance level recommended may now have been superseded by newer specifications.
Q. Does using the right motor oil have anything to do with engine life ?
Ans. The single most important thing you can do to get long life from your engine is to change your engine oil and oil filter as often as recommended by your car manual. This is good maintenance practice. Note that a motor oil that properly lubricates the engine system during the first few thousand kilometers can later become thick and even corrosive after long periods of use. It then cannot flow as required and also blocks the oil filter. This may cause engine damage and seizure in extreme cases. Draining off used oil, following the vehicle manufacturer's recommended oil change intervals, also removes abrasive metal particles.
Q. Why do oil companies sometimes recommend more than one product for the same application ?
Ans. Different drivers and different motoring conditions call for different oils. Thus, a car that is driven under very arduous conditions, with a lot of high-speed motoring, may be better lubricated with a synthetic oil which can better resist the high temperatures.
Q. Why are some oils called synthetic and others mineral ?
Ans. This refers to the origin of the base fluid. Mineral oils are derived by refining processes, essentially a complex series of purification and separation steps, from crude petroleum oil extracted from the ground. Synthetic base fluids are made by chemical processes, generally by building up larger molecules from smaller ones. Because these chemical reactions and starting materials are well defined, the synthetic fluids are not only relatively pure chemicals but are deliberately made to deliver the performance characteristics required in a lubricant.