How to choose an engine oil?
Lubrication, cleaning, corrosion inhibition: engine oil is essential for your vehicle to run smoothly. How to choose an engine oil? What are the key criteria? Mineral or synthetic, viscosity index, standard: see all the information you should consider before selecting your product.
Choosing an engine oil: synthetic or mineral?
When choosing an engine oil, you must first know the type of oil you need. Mineral oils come from the refining of petroleum; synthetic oils are obtained by mixing several synthetic components. Semi-synthetic oils are a blend of mineral oil and synthetic oil. It’s the nature of the product that defines its viscosity (we often speak of its “grade”).
Viscosity is the index that defines the capacity to resist oil flow when hot and when cold. Engine temperatures can reach as high as 400°C, so this is a key criterion when choosing your product. It is marked as follows on the oil container: 00w00. The number on the left is the low-temperature viscosity. The lower the number, the more the product is efficient at low temperatures. The number on the right indicates oil performance when hot. The higher the number, the more the oil is efficient when subjected to high temperatures.
Obtained by refining petroleum, they are generally used on “conventional” engines, older models, or engines without turbochargers. They are thicker than synthetic or semi-synthetic oils and are recommended for driving in temperate climates (they are not compatible with extreme temperatures). Their oxidation stability is lower than for other types of engine oils, so they need to be changed more frequently than synthetic oils. Their main advantage is their lower cost.
They are a blend of mineral oil and synthetic oil. By adding synthetic oil to mineral oil, performance and protection are improved. Semi-synthetic oils therefore offer a good quality/price ratio. Their use does not affect the frequency of oil changes.
Chemically modified to increase their performance, synthetic oils contain fewer impurities than mineral oils and are therefore of better quality. They are designed for high-performance engines, making them more suitable for more modern vehicles, and for motorsport. Synthetic oils facilitate cold engine starts while withstanding high operating temperatures. They also optimize engine maintenance. You can go longer between oil changes, for both diesel and petrol engines.
Standards to know when choosing an engine oil
When choosing an engine oil, you can also refer to the standards of the product. This information allows you to:
- know the type of engine the motor oil is designed for (diesel or petrol
- know its performance level;
- know if the oil meets your automotive manufacturer’s recommendations
On the current market, three standards are used to describe engine oils.
The ACEA standard
This is the standard of the European Automobile Manufacturers' Association (“Association des Constructeurs Européens Automobile” in French). It is a quality indicator that is determined by a letter and a number (e.g. A1). The letter indicates the type of engine:
- A: oil designed for petrol engines;
- B: oil designed for private car diesel engines;
- C: for light engines equipped with catalytic converters or particulate filters;
- E: for commercial vehicles and trucks.
The number indicates the specific performances the oil must provide.
ACEA 2016 defines
- 3 category combinations for petrol and diesel engines: A3/B3, A3/B4, A5/B5
- 5 categories for vehicles with a pollution control device: C1, C2, C3, C4, C5
- 4 categories for commercial vehicles and trucks E4, E6, E7, E9, of which two are for vehicles with a pollution control device: E6 and E9.
The SAE standard
Determined by the Society of Automotive Engineers, this standard describes the degree of oil viscosity. It is indicated on the front of the container: the 00w00 index.
The API standard
Established by the American Petroleum Institute, it classifies the product according to several criteria: dispersive power, and protection against wear, oxidation, corrosion and detergents. The standard consists of two letters: S for petrol engines, or C for diesel engines. The second letter indicates the oil’s performance. The “further” the letter is in the alphabet, the higher the quality of the oil. For example, an SH oil will have a lower performance than an SN oil.
To know the standard required for your vehicle, see your vehicle owner’s handbook or get advice from a professional.