ONE of the most common maintenance items that we do is changing the oil in our cars. It is also one of the most confusing subjects to discuss about with your foreman. Which oil is best? Should I go for the mineral or synthetic? When should I change the oil? Should the filter be changed as well? Is my foreman making more commission from this particular brand (sensitive question)?

While your foreman or workshop may be under pressure to sell you a particular brand of oil, it is your right to know exactly what you are buying and using. Read on so you can make an informed decision about this most slippery of subjects.

The first thing you should do is to find out what oil is recommended for your car. Obviously your car manual will state this or you can go online to find out. However, some cars may be older and use older standards and designations. This is not particularly important as the standards and designations are updated regularly. What you must adhere to is only the viscosity of the oil and the quantity stated for your car.


All oils are tested and given a designation. One of the most common is the American Petroleum Institute (API) and Society of Automotive Engineers (SAE) although some have both API, SAE and Japanese Automotive Standards Organisation (JASO) designations. In addition to the standard, there is usually a two character designation like SL or MA as well. This means that the oil has been tested to a separate group of tests. Sometimes you will see a year designation which indicates the standards’ year of issue. Standards get stricter and more tests are added every few years so the later the date the better the oil. Diesel engine oils get an additional letter like C added on.


The recommended oil for your car will state an SAE designation such as SAE 10W30 or 0W50. The SAE designation is to determine the oil’s viscosity. Viscosity is a fluid’s resistance to flow and with oils the rating starts at 0∞ F (represented by the number preceding the W for Winter) and at 212∞ F (represented by the second number in the viscosity designation). Oil thins as it heats and thickens as it cools. And the designation states how this particular oil reacts at those temperatures. But you need the oil to flow well when the engine is cold and not thin out when the heat gets high. That is where additives come into the picture. Many oils are blended with additives to improve the oil’s performance. And synthetic oils have higher performance than mineral-based and semi-synthetic oils. The most important thing to remember is to keep to your recommended viscosity for your car.


Generally, there are three types of oil, Mineral, Semi-Synthetic and Fully Synthetic. All of these engine oils are produced from 5 types of petroleum base oils, of which some are more highly processed than others. The most highly processed are altered so much so they are not considered natural oils but are called synthetics. The base oil package in any oil makes up anywhere from 70 to 95 percent of the mix, the rest are comprised of additives. Every oil manufacturer has their own recipe of additives for their oil. More additives equals a higher price, naturally. More about additives later.

CONVENTIONAL MINERAL OIL: All leading brands have mineral oils available in several viscosities. A 5W-20 or 5W-30 oil is for lower temperatures and a 10W-30 oil is particularly for higher ambient temperatures. Stick to your recommended rating.

SEMI-SYNTHETIC OIL: These are synthetic oils mixed with mineral oils and are formulated to provide protection for heavier duties and higher temperatures that conventional mineral oils. Generally this means they’re less volatile which reduces oil loss and increases fuel economy.

Fully Synthetic Oil: Made for high-tech and high performance engines, these oils pass stringent special tests (usually indicated on their labels), and it also means they have superior, longer-lasting performance in all the critical areas, from viscosity index to protection against deposits. They flow better at low temperatures and maintain peak lubricity at high temperatures.

HIGHER MILEAGE OIL: A new development in oil technology and marketing. Since today’s vehicles last longer, the oil companies formulated this oil for higher-mileage vehicles. The higher-mileage oils are formulated with seal conditioners that help plug up oil leaks in an older engine. Some may have additives like viscosity-index improvers in them for better piston-to-cylinder clearances, and antiwear additives to try to slow the wear process.

More important is changing the oil and filter regularly. Your manual will also state these intervals but if you must, the absolute minimum is twice a year(!). If your car has an electronic oil-change indicator on the dashboard, follow it.


High engine temperatures, moisture, combustion by-products, rust, corrosion, metal particles and oxygen all conspire to produce sludge and varnish in oils. Additives not only assist oil in maintaining good lubrication, they also help minimize sludge and varnish and reduce any damage from their formation.

• Viscosity-index improvers: Reduces the oil’s tendency to thin at high temperatures.

• Detergents: These remove deposits but their main purpose is to keep the surfaces clean by inhibiting the formation of high-temperature deposits, rust and corrosion.

• Dispersants: This additive disperses solid particles so they don’t form sludge, varnish and acids. Some additives work both as detergents and dispersants.

• Anti-wear agents: Anti-wear agents protect the metal surfaces if the oil surface breaks down.

• Friction modifiers: They reduce engine friction improve fuel economy. Graphite, molybdenum and other compounds are used.

• Pour-point depressants: These additives help the oil flow readily at low temperatures. Oil contains wax particles that can congeal and reduce flow, so these additives are used to prevent it.

• Anti-oxidants: Anti-oxidants are needed to prevent oxidation (and, therefore, thickening) of oil. Some of the additives that perform other functions also serve this purpose, such as the antiwear agents.

• Foam inhibitors: Foam inhibitors are used to cause any foam bubbles in the oil to collapse readily.

• Rust/corrosion inhibitors: Protect metal parts from acids and moisture.

Not all additives are good, though. Some oils have sulphur compounds which have good anti-wear and anti-oxidation characteristics, but they can reduce fuel economy and affect catalytic converter operation. Too much of a particular detergent could affect the anti-wear characteristics. Too much of a specific dispersant could affect catalyst performance and reduce fuel economy. Anti-wear and friction-reducing additives also may have ingredients (such as sulphur) that could also affect catalyst performance.

But in the end, your car’s manufacturer will have stated the correct viscosity, quantity and intervals. Stick to this and you won’t go wrong. When it comes to oil, it simply boils down to how much you are willing to spend. See you at the next service

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