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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

11. What are Bio-Fuels ?

These are liquid fuels used for road transport (e.g. cars, buses and trucks) which have been made from a plant (occasionally) animal source. They fall into two general categories: bio-alcohols - mostly used for spark-ignition engines which otherwise burn petrol; and bio-diesel - mostly derived from vegetable oils and used in diesel engines in trucks and buses (and some cars). The aim of bio-fuels is to replace oil-based fuels that are derived from petroleum, a dwindling natural resource, with fuels from renewable sources, such as plants

12. Why are Bio-Fuels so popular these days ?

For some consumers the concept of sustainable resource management is important, and this is also linked to the fact that use of bio-fuels decreases the overall rate of release of carbon dioxide (a greenhouse gas) into the atmosphere. These benefits have also attracted the attention of governments and other political bodies. Targets for their use (e.g. a % of total fuel used should be from a renewable source) have been set in some countries. In these countries there is usually a tax advantage applied to bio-fuels, in order to stimulate their use through cost-reduction.

13. Can I use Bio-Fuel in my vehicle ?

A car (or motorcycle) with a petrol engine (spark ignition) can use gasohol (gasoline containing up to 20% bio-alcohol) without modification. For higher percentages of alcohol the engine, ignition and fuel systems has to be modified, or a Flex-Fuel or dedicated alcohol-engined car used. This is because alcohol contains less energy per litre than gasoline, so a greater fuel volume has to be burnt for the same distance travelled. On the other hand, alcohols have a very high octane rating, which, combined with higher engine compression ratios, gives a higher engine efficiency. In many countries the unleaded gasoline specification (for ULG 95) allows the addition of up to 5% bio-alcohol as a blend component. Alcohol is blended into the gasoline, by the fuel company, in order to boost the octane number and so many motorists are already using bio-alcohol without even knowing it.

Diesel engines can burn bio-diesel without any modification to the engine or fuel system. In fact, when Rudolf Diesel invented the diesel engine, he used peanut oil as t he fuel. Correctly speaking, bio-diesel is the methyl or ethyl ester of a vegetable oil (or animal fat), and NOT unprocessed vegetable oil. This difference is important, the esterification reaction lowers the fuel's viscosity so that it forms a good aerosol spray when injected into the engine. Engines which are run on unprocessed vegetable oil run the risk of injector fouling and worse mechanical problems. As with bio-alcohol, bio-diesel is often sold blended with diesel fuel from petroleum, e.g B10 (10% bio-diesel 90% automotive gas oil). This type of bio-diesel is just as good as normal diesel fuel.

14. Are Bio-Fuels safe to use ?

Yes, as long as you are using a fuel suitable for your vehicle and the fuel is from a reputable supplier. You should be aware, however, that:

Bio-alcohols are flammable liquids and burn with a virtually invisible flame

Methanol (a bio-alcohol) is very toxic

But bio-alcohols blended with gasoline (i.e.gasohol) is relatively safe.


Bio-diesel is safe to use

15. Can I buy Bio-Alcohol ?

In some countries you can buy gasoline already containing bio-alcohol as a blend component. You will probably not be informed of the presence of bio-alcohol in this case, as the fuel is sold as normal gasoline. In a few countries you can now buy bio-alcohol as a fuel in its own right. This is typically 85% alcohol (in USA and Europe) and suitable ONLY for cars designed to use bio-alcohol (e.g..Flex-Fuel cars). In Brasil you can buy "alcool hidratado", which is 85-93% ethanol and again destined for use only in Flex-Fuel cars or dedicated alcohol fuel cars (which have very high compression ratio engines).

16. Can I run my car on Bio-Alcohol ?

f you buy E85 (85% ethanol) then you must have a car designed to use bio-alcohol (Flex-Fuel or dedicated alcohol car). You cannot readily retro-fit the fuel handling systems onto a normal gasoline-engined car to then accept bio-alcohol fuel.

17. Can I buy Bio-Diesel ?

In many countries you can buy B5 or B10 bio-diesel (5 or 10% bio-diesel in gas oil). In a few countries B100 is available. Avoid buying fuel made from unprocessed vegetable oil.

18. Can I run my car on Bio-Diesel ?

Yes, but only if it is a diesel-engined car. Both B5 and B10 are suitable for virtually every diesel engine; in cars, vans, trucks and buses. If you sue B100, then you should check with the manufacturer of your vehicle. It is quite likely that the service and oil drain intervals will be shorter.

19. Can I make Bio-Diesel for my own use?

It is possible, but Gulf Oil International does not recommend this.  You have to handle dangerous chemicals (methanol is very toxic, caustic soda or potash is very corrosive) and you have to dispose of the hazardous waste safely. You will need to find a use, or buyer, for the glycerine by-product (or dispose of it in a safe manner).  You will need to take good care of the quality of the process, to ensure complete esterification and purification of the bio-diesel. This is even more difficult if your raw material is used cooking oil, which will be of inconsistent composition and have many impurities.

20. Will Bio-Fuels prevent global warming ?

one of the causes of the climate change commonly known as  global warming is the rise in the amount of carbon dioxide in the atmosphere. This gas allows radiation from the very hot sun's surface to penetrate through to the earth, but reflects the longer wavelength heat radiation given off by the cooler earth surface. carbon dioxide is largely a by-product of fuel combustion, principally coal and oil, in man;s quest for more and more energy.

All vehicle engines burning bio-fuels emit carbon dioxide, which is an important greenhouse gas and a cause of global warming, just as they would if running on regular oil-derived gasoline or diesel fuel. But the plants used to generate the bio-fuel absorbed carbon dioxide from the atmosphere - an essential element of the bio-synthesis process. Thus, on an overall balance, use of bio-fuels instead of petroleum reduces the amount of carbon dioxide being added to the atmosphere (per vehicle-kilometre driven). In Brasil where nearly 50% of the fuel used in cars is bio-ethanol, the overall national carbon dioxide emissions have been reduced by 13% (compared to a baseline case where no bio-fuel would be used).

So, bio-fuels themselves will not stop global warming, but their use will mitigate one of the principle causes.

21. 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.

22. 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.

23. 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.

24. 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.

25. 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

26. 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.

27. 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.

28. 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.

29. 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'

30. 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.





Oxidation Inhibitor

Prevents varnish and sludge formation on bearings or in circulating systems. Retards aging of the oil. Lengthens service and storage life of oil. Protects oil itself directly (indirect protects metal parts - varnish and acids) 

Reacts more readily with oxygen (from air) than does the oil itself, thereby retarding oxidation of the oil. Inhibits the formation of free radicals, an important chemical species in the oxidation process, thus slowing oxidation reactions

Rust Inhibitor

Prevents rusting of ferrous (iron or steel) machine parts

Forms a film on ferrous metallic parts thus protecting them from attack by water and air, or other destructive material.

Corrosion Inhibitor

Prevents corrosive attack on non-ferrous metallic surfaces

Forms a film on non-ferrous metallic parts thus protecting these parts from attack by contaminants in the oil.


Prevents oxidation products (sludge) which have formed in oil from sticking to metal components. May also remove deposits already formed on metallic components. Usually combined with dispersant additive   They are also used to neutralise acids which form in the oil, or are introduced as by-products of fuel combustion.

By chemical reaction, oxidation products (sludge) remain soluble in the oil and do not stick to the metal surfaces. Chemically neutralise acids.


Keeps oxidation products separated and suspended in the oil. Retards formation of sludge

By chemical reaction, oxidation product particles are kept small enough to allow them to float in the oil.

Foam Inhibitor

Causes foam to dissipate more rapidly

Protects combination of small bubbles into large bubbles which in turn burst more easily.

Viscosity Index (V.I.) Improver

Reduces rate of change of viscosity with temperature

Additive thickens with increasing temperature thereby preventing oil from thinning out too rapidly

Pour Depressant

Lowers the Pour Point

Keeps small wax crystals apart thus preventing the formation of large crystals which would stop the flow of oil.

Anti-wear agent

Minimizes wear caused by metal-to-metal contact during conditions of mild boundary lubrication e.g. starts and stops

Additive reacts chemically and forms a film on metal surfaces under normal operating conditions

Extreme Pressure (E.P.) Agent

Prevents welding and subsequent wear or seizure of contacting metal parts under extreme or shock load conditions.

When metal-to-metal contact occurs (as under extreme or shock load conditions), the heat generated at the point of contact causes the additive to react chemically with the metal. The new compound formed between the metal surfaces reduces friction and prevents welding or seizure.

Tackiness Agent

Increases the adhesive properties of a lubricant - improves retention and prevents dripping and spattering

High molecular weight compounds are added to the oil thereby increasing its viscosity and improving its adhesive properties.


Promotes rapid mixing of water and oil resulting in the formation of a stable emulsion (e.g. water-soluble cutting oils)

Reduces interfacial tension and permits intimate mixing of oil and water.


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