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Frequently Asked Questions (FAQs)

1. What is a modern lubricant?

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.

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2. What is viscosity?

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 judgement of the operator.

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3. What is an SAE grade?

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.

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4. What is a multi-grade oil?

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 minimise this effect. Multi-grade oils are defined by a viscosity rating at a low temperature, as well as one at 100 C.

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5. We have come across an oil having a 20W-40 rating. What does 'W' stand for?

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.

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6. What does the specification API stand for?

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.

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7. How do I choose the right oil for my vehicle?

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.

Gulf Oil International has, on this website, a large database of cars, trucks, buses which will show you the Gulf recommended products. Furthermore, you can always contact your nearest Gulf representative who should be able to provide you with advice.

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8. Does using the right motor oil have anything to do with engine life?

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 kilometres 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.

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9. Why are some oils called "synthetic" and others "mineral"?

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

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10. Why do oil companies sometimes recommend more than one product for the same application?

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.

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11. How is a Lubricant made?

A lubricant is made in a blending plant. There, the base oils (which may constitute up to 99% of the lubricant, by volume) are mixed together with specially selected additives. Before blending, the base oil is purified by filtration and removal of water; after blending the finished product is subjected to quality control checks in the plant's laboratory before being approved for packing and dispatch.

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12. What is a base oil?

Base Oil (sometimes also called base stock) is the name given to the main liquid component (or components) of a lubricant. It is. Base oils are mineral (or petroleum) or synthetic in origin, although vegetable oil-derived stocks may be used for specialised applications. The base stock provides the basic lubricating requirements of a lubricant.; i.e. the "oiliness".


However, in most modern lubricants a base oil mixture alone is insufficient to deliver the technical performance characteristics required and to keep the product from rapid degradation in use. Therefore the lubricant manufacturer will mix the base oils with a variety of different additives, each chosen to impart additional performance benefits to the finished oil.

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13. What are the different kinds of base oils?

Base oils are be classified by both viscosity and their generic chemical composition, itself a function of the original crude oil and/or the refining process. Depending on the proportions of hydrocarbon molecule type: base oils can be either paraffinic, naphthenic or aromatic in nature. There are several widely used viscosity classifications, of which the term ?solvent neutral' is the most common, e.g. SN 150 and SN 500, where the number represents the SUS viscosity (measured in Saybolt Universal Seconds at 40 C). Base oils are also classified by their viscosity index (a calculated figure based on the viscosities measured at both 40 and 100 C). Thus oils are either Low Viscosity Index (LVIs) or Medium Viscosity Index (MVIs), High Viscosity Index (HVIs) or extra High Viscosity Index (XHVIs). The higher the viscosity index, the less the oil will ?thin down' upon heating, and the less it will ?thicken up' upon cooling.


Base oils are also be defined by the type of refining process used: solvent extraction (for solvent neutral oils) is widely used, but more highly refined oils can be made by a hydro-finishing process or by hydro-cracking.

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14. What are synthetic base oils?

Synthetic base oils are chemicals that have been made, or synthesised, by combining several smaller molecules together. There are several different types, each with its own suite of physical and chemical properties, and each ideal for a selected set of uses in lubrication. Because these are ?made to design', and are usually quite pure in composition, the lubricants they are used in can have specific properties which cannot easily be achieved though the use of mineral base oils. This advantage, though, comes at a higher price.

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15. Are synthetic oils better than conventional motor oils?

In most cases the answer is "yes". Synthetic oils are man made lubricants which were originally created for jet aircraft engines. They have a wide range of performance and can protect engine at very high and very oil temperature conditions. In other words, they have exceptional thermal stability.


The main disadvantage of synthetic lubricants is that they are inherently more expensive than mineral oils. This restricts their use to speciality oils and greases which command premium prices. Coincidentally, oil marketers therefore ensure that their synthetic oils are also capable of the highest performance possible

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16. Where are these synthetic base oils used?

The main advantages of the synthetic oils are in their high viscosity indexes, higher flash points, lower pour points and very low volatility (tendency to evaporate at higher temperatures) This makes them valuable blending components when compounding for extreme service at both high and low temperatures.

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17. What are hydrofinished base stocks? What other kinds of base oils are available in the world?

The list is extensive. Hydro-finished base oils are mineral oils that have been subjected to a light hydrogenation treatment to remove certain impurities that could affect the oil's chemical stability. There is a long list of synthetic fluids used to make lubricants; poly-alpha-olefins, long chain organic esters, phosphate esters, poly-glycols, poly-alkylbenzenes are the most common.


New refineries are being built in which natural gas (methane) is converted into liquid fuels (gasoline, diesel fuel), and a useful by-product will be heavier hydrocarbon molecules which can be used in lubricants. These gas-to-liquid base stocks are expected to have properties similar to some of the synthetic molecules now used, but be available at a much lower cost.

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18. Can synthetic oils be used for longer periods, or will they prolong the engine's life?

It is always best to follow the vehicle manufacturer's (the OEM's) recommendation for oil drain periods. Some OEMs do permit extended drain intervals when high quality, high performance synthetic oils are used. This is often done in combination with extended vehicle and engine service intervals, as it is in the OEM's interest to ensure the engine and the oil will require servicing after longer and longer intervals.


However, because most oil marketers ensure that their expensive, synthetic oils are also the best in terms of performance, when only a normal oil drain interval is observed the oil will give excellent protection to the engine and thus contribute to extended engine life.

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19. Why are additives used in lubricating oil?

Additives are used in lubricating oil to change or alter or enhance its properties. Base oil as such cannot be used in most of the present-day lubricating applications. Their properties - like resistance to heat, oxygen, wear etc - have to be increased. This increment is done with the use of these additives. To increase the resistance to oxidation, we add 'antioxidants', to increase resistance to wear, we add 'anti-wear additives'

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20. What are these additives?

The list below covers most of the additives used. You can see that lubricant formulation is a real science as there are many components and variables, all of which must be balanced out to make a well-rounded product, which is then proven by a series of rigorous tests.

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