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Engine oil has 5 main roles:
1) Lubrication: reduces friction between the moving parts, prevents wear and over-heating.
2) Cooling: removes the excess heat from the engine.
3) Cleaning: absorbs temperature deposits and particles results by engine running
4) Sealing: seals the engine combustion chamber
5) Preservation: prevents corrosion and rust
A good quality engine oil and in the right quantity is essential to extend the engine life. Without fuel the engine will stop running; without oil the engine will collapse.
There are three major parameters that differentiate between the oils, and information on each parameter is givenby the letter symbols on every container.
1. The viscosity of the oil
Oils with low viscosity are liable to be thin at high temperatures and thus lose their lubrication layer. On the other hand, oils having too high a viscosity may be too thick at low temperatures, which means they will flow slowly to the upper parts of the engine head, not properly penetrate all the moving parts, and even lose their lubrication layer at high RPM.
2. The type of oil: mineral, synthetic, or semi-synthetic
Mineral engine oil − The most widely used oil. Its performance is standard, and it does not optimally meet the standards required for modern engines. It comes with relatively high viscosity.
Semi-synthetic engine oil − As its name says, it is a mixture of mineral oil and synthetic oil. This is oil of good quality, suitable for the needs of advanced engines, and it meets the requirements of the vehicle manufacturers.
Synthetic engine oil − This is produced in accordance with the strict requirements of the vehicle engine manufacturers. This is the oil currently recommended for use in today’s hi-tech engines. It is intended to ensure a very long life and thus extend the time between oil changes, even under hard working conditions. In addition it meets the requirements of the environmental standards.
3. The quality of the oil
The most widely used classifications in the world are those of the American Petroleum Institute (API) and the European Automobile Manufacturers Association (ACEA).
The answer to this question is complex and depends on the specific vehicle model that you own. Vehicle manufacturers provide vehicle owners with a handbook that gives detailed lubrication instructions, including the quality required and the grades of viscosity suitable for various environmental conditions. In many cases the vehicle owner’s handbook suggests alternatives for both the oil specifications and the levels of viscosity. Adhere to them and also to the instructions regarding the frequency of oil changes.
Anything, between “nothing” and “irreversible damage to the engine”. It depends on the extent of the unsuitability. We recommend you don’t try and find out. If you’re worried that you’ve used an unsuitable oil, you should go to your service garage as soon as possible for a proper oil change, and check that they do it according to the manufacturer’s instructions.
They refer to two parameters: viscosity and standard. It goes like this:
Viscosity: The viscosity values have been specified by the American Society of Automotive Engineers (SAE), and consequently these viscosity values are marked SAE on the oil container. Most engines use multi-grade oil, that is an oil that changes its viscosity in accordance with the working temperature of the engine. The first digit on the left indicates the viscosity of the oil when cold (you can identify it by the letter W – Winter) and the digits on the right indicate the viscosity of the oil when hot. For example, 5W-30.
In general, the lower the first number, the better the oil will function in very cold weather; and the higher the second number, the better the protection it will give at higher temperatures. The range of viscosity is important since the oil must be suitable for both stone cold engines and after they have been running for some time. Despite this, for certain types of modern engines some manufacturers demand even lower viscosity values, such as 0W-20.
Standards: The most widely used classifications in the world are those of the American Petroleum Institute (API), the European Automobile Manufacturers Association (ACEA), and the specific specifications of the various vehicles manufacturers. The standards of the American Petroleum Institute are relevant for vehicles sold in the US and for the working conditions there. The current highest classification of the American Petroleum Institute is API-SN for petrol engine oil, or API-CJ-4 for diesel engine oil. The letter S indicates a petrol engine and the letter C indicates a diesel engine. Types of oil suitable for both kinds of engine are labeled with both sets of letters, e.g. SN/CF. By the way, the letter S stands for Service station, while C stands for Commercial.
In Europe most of the oils are defined by the ACEA, that divides engine oil into four groups: ACEA-A for petrol vehicles, ACEA-B for light diesel vehicles, ACEA-C as suitable for a catalytic convertor, and ACEA-E for heavy diesel vehicles. The letters are followed by a number: 1,2,3,4,5 for passenger vehicles and 6,7,9 for heavy vehicles. (By the way, a higher number does not mean higher quality.) The European specification currently refers to the A,B standards together. In other words, the same oil is suitable both for petrol engines and light diesel engines.
Two standards are generally shown on oil containers made in Europe, the Far East, and the Middle East: the European and the American.
In the distant past it was customary to use different oils for petrol engines and diesel engines. Today most engine oils are suitable for both petrol engines and diesel engines. Consequently they are marked with a combination of letters, such as SN/CF or SM/CJ-4.
Generally not. The viscosity of the oil is determined by the requirements of the manufacturer that vary with the model and the production year of the specific engine, and it does not necessarily indicate the quality of the oil. As evidence: tables are given in the vehicle owner’s handbook that specify the different viscosities required in different geographic regions depending on the ambient temperature, even when dealing with the same model.