What oil Choosing the right engine oil for your car

Updated: Nov 2 2013, 21:18pm hrs
Engine oilIt's the engine oil that protects the innumerable parts contained inside an engine and helps it run smoothly.
Apart from the fuel that it consumes, there is one important liquid that your cars engine needsengine oil. But with cars getting better with successive generations, we, as owners, dont really even have to look under the hood any more. As long as it is being serviced it should run fine, right

But isnt this taking things for granted What if youre being charged for unnecessarily expensive engine oil when it isnt required Should you continue to spend more money every oil change for no real benefit How would you know the difference Imagine the low oil warning lamp came on. Would you know what grade of oil to top up with Its not as easy as youd imagine it. Read on to find answers to these and many other questions relating to this seemingly simple liquid.

An engine contains innumerable parts, mostly metal, that work together to produce power to move the car by burning fuel. These parts are made to withstand potentially destructive explosions within the engines confines created because of the continuous mixtures of air and fuel, and the resulting vibrations and heat that is generated. And the engine is expected to perform at its peak all the time. Its the engine oil that protects these parts and lets them run smoothly.

The role

The main job of the oil is to lubricate the engines internals and keep the friction between them to a minimum. For example, pistons move to and fro at high speeds inside each of the engines cylinders and the greater the friction between the piston and the cylinder wall, the greater will be the energy required to overcome it. The engine oil forms a film between the metal parts to help them move freely. The oil also helps keep the temperatures in check as it absorbs the heat from the metal parts of the engine.

Then theres the build up of hydrocarbon deposits within the engine because of the burning of fuel and the reaction with the impurities brought in by the air intake system. The oil also rids the engine of these (via the air filter) and keeps them away from the moving parts, thereby cleaning the engine. For this, there are some cleaning agents added to the oil as well.

Why change engine oil

With use, the oil loses its lubrication properties and picks up bits of metal particles, and this leads to a decline in its performance. This decline can be caused by a number of factors, and heat is a big one. The oil is made up of a number of different ingredients, each with a different molecular structure (especially mineral oils). The lighter compounds among these evaporate quicker at high temperatures and leave behind the denser ones. This leads to a change in the thickness of the oil and, consequently, its ability to move freely and lubricate the engine.

Another reason the engine oil deteriorates is the accumulation of contaminants. These include dirt from the air intake system and tiny metal particles from the wear and tear of engine parts. Then there are the by-products given off by the combustion of fuel. These are generally carbon based and lead to the formation of sludge. All these impurities get collected and impede the oils ability to flow smoothly and consequently, its ability to lubricate.

If the oil cant perform like it is meant to, it can lead to engine damage. This is why engine oil should be changed regularly. Car manufacturers recommended oil change intervals are based on distance covered or your odometer reading, and its a safe bet to follow this. Still, you should also periodically check the engine oil quantity and quality yourself, using the dipstick, and change or top up if necessary. And remember, an early change is always better.

Types of oil

When it comes to the type of engine oil you put in your car, you have three optionsmineral oil, synthetic oil and semi-synthetic or blended oil. Mineral oil is extracted from crude oil just like petrol and diesel, but while the fuels are extracted from the more volatile constituents, mineral engine oil is made up of more stable and heavier components; those that burn at much higher temperatures. Mineral oils are the cheaper option, with prices starting from as low as R300 per litre.

Synthetic oils are based on mineral oils and contain compounds of similar density and structure, but they are highly refined, and therefore offer better lubrication. Synthetic oil is recommended for high-performance engines and are relatively expensive, with prices starting from R1,000 per litre. However, they do have benefits over mineral oils.

Blended or semi-synthetic oil, as the name suggests, is a mix of the above two. Generally speaking, the mix will contain more mineral oil than synthetic, and its worth checking, because blended oils are often classified as synthetic oil by manufacturers. Prices of blended oils, on average, start from R450 per litre.

Grades & classifications

Now that you know what kinds of oils are available, you also need to know which grade and service classification suits the engine in your car. These are nothing but a description of the oils fluid properties and performance capabilities.

Before we go ahead, we have to understand what viscosity is. In simple terms, its the thickness of a fluid. For example, water is less viscous than Fevicol. And the grade of the oil refers to its viscosity at normal operating temperatures.

For oils, a rating by an organisation called the Society of Automotive Engineers (SAE) is used, and is represented by numbers like 0, 5, 10, 15, going on to 60. The higher the number, the greater the viscosity. Now, here too, temperature has a part to play. The majority of an engines wear and tear happens when you start the car, because the engine is at its coldest. However, once the engine is warmed up and spinning faster, you need oil with different properties. Previously, you could only get single-grade oils, with a constant viscosity across all operating temperatures. These days, however, most oils are of the multi-grade variety. These exhibit varying viscosity at varying temperatures and have a two-number rating, such as 10W40.

The W in the rating stands for Winter, and this refers to its cold-running viscosity rating. In this example, the oil will have a viscosity of a 10-grade oil at lower temperatures and a 40-grade oil at higher temperatures. But bear in mind that a 10W40 oil and a 20W40 oil will both have the same viscosity at the engines optimal operating temperature.

Oil manufacturers will also give a service rating for the oil. These ratings certify that the oil meets certain performance and quality criteria and has been tested for standards like high-temperature deposit protection and sludge control. These ratings are either issued by the American Petroleum Institute (API) or Association des Constructeurs Europensd Automobiles (ACEA).

The API standards for petrol engine oils have an S- rating, while the diesel engine oils have a C- rating. The current highest ratings are SN and CF. The ACEA standards are A- and B- for petrol and diesel engine oils respectively, with the current highest ratings of A5 and B5. The ACEA also has a C- rating for cars with Diesel Particulate Filters (DPF) and Three Way Catalysts, and the current highest rating is C4.

To know what grade and service rating of oil your cars manufacturer has recommended, have a look at the car owners manual.

Whats in the can

The engine oil you buy is not as simple as promoted by manufacturers. A lot of research and development goes into it and the final product is a concoction of a lot of ingredients, especially mineral oils. Some of the important ones are:

* Base oil: The major part of any engine oil; this is what gives the engine oil its main characteristics. These base oils can be of two types; refined natural oil (mineral oil) or highly refined (synthetic oil). A mix of these two is also available (semi-synthetic or blended oil).

* Detergent: Yes, you read it right, there are detergents in the oil, but not the kind you wash clothes with. These are organic materials and can be either acidic or neutral in nature. These help clean the engine and prevent carbon deposits from taking a hold.

* Corrosion inhibitors: These protect the engine from getting corroded by oxygen, water and acids. The inhibitors stick to the engine and prevent the above mentioned from acting on the exposed metal surface.

* Viscosity index improvers: The physical properties of the oil change because of the change in temperature from a cold start to the optimum working temperature which can be around 100 degrees.

* Anti-oxidants: These constituents of the oil are meant to react with oxygen and prevent corrosion.

* Conditioners and friction reducers: These are wax-like in nature and stick to the engine to improve the lubricating effect of the oil.

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