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Engine oil: all you need to know

Updated: Jan 16, 2022

The vehicles we drive all require regular maintenance. The most common is to change the engine oil. It is essential for the proper functioning of the vehicle, its performance and the longevity of its engine.

There are a multitude of engine oils on the market with different characteristics and if you are wondering which one to buy for your car and when to change it, COCKPIT will explain it all to you.


1 / What is the role of engine oil?

The primary role of an oil is to lubricate the parts of the engine which are connected. It makes it possible to limit the friction between the parts, friction which not only generates heat production (and therefore a loss of power) but also causes wear of the parts.


2 / What are the different types of engine oils?

Engine oil is made up of 60 to 85% base oils. They can be of mineral origin (refining of crude oil) or of synthetic origin (they are produced by chemical synthesis).

Semi-synthetic oils are the mixture of mineral bases with a synthetic base.

The role of performance additives is to reinforce certain fundamental properties or to compensate for certain weaknesses of base engine oils.

The additives provide properties such as protection against wear and resistance to extreme pressure, detergency, dispersion of pollutants, protection against corrosion, resistance to oxidation, etc.


3 / What is the viscosity of the oil?

Viscosity is a measure of resistance to the flow of a fluid. The viscosity of an engine oil is expressed by 2 grades: the cold grade and the hot grade.

The cold grade is located in front of the letter W (Winter). In the illustration opposite, the grade is 10. The hot grade is located after the letter W. In the same example, the hot grade is 40.

The 1st grade reflects the dynamic viscosity when cold: the ability to start the engine and prime the oil pump: 0W: approx. -30 ° C 5W: approx. -25 ° C 10W: approx. -20 ° C 15W: approx. -15 ° C

The 2nd grade reflects the kinematic viscosity when hot (100 ° C and 150 ° C under shear): 20, 30, 40, 50, 60. The higher the number, the thicker the film of oil when hot. It promotes protection and waterproofing. The lower the number, the better the hot friction reduction will be. It promotes fuel economy. To ensure immediate protection each time the engine is started, the choice of cold viscosity grade is essential. The more fluid oil is the fastest for the engine oiling time.

If the oil is too fluid, it no longer does its job, even if it is not sufficiently fluid, the pump can no longer circulate it in the circuit.


4 / What are the standards for oils?

Each car manufacturer sets its own standards depending on the vehicle in question. We find its standards mentioned in the manuals of use and maintenance of vehicles. They are also on the back of the container.

There are two main types of classification:

- The SAE Standard: The need for a simple classification system for motor oils at an international level gave rise to the "Society of Automotive Engineers" or SAE which developed a system which bears its name. This system only defines viscosity categories.

There are two categories, ie "summer oils", indicated by the numbers SAE 20, 30, 40 and 50 and so-called "winter" oils indicated by SAE 0W, 5W, 10W, 15W, 20W and 25W. These mainly refer to power to provide satisfactory results at cold start. The following table gives a summary of the viscosity limits at the temperatures considered. Please note: summer oils always at 100 ° C, winter oils at different (low) temperatures.

This standard is in the forms "ACEA B3 / B4", "API CF / DF", "VW 500.01" ... These letters and numbers make it possible to determine whether an oil is made for a gasoline or diesel engine, to assess its level of performance and whether or not to meet certain recommendations specific to each manufacturer.

- API classifications (American Petroleum Institute): This two-letter classification classifies engine oils according to their qualities and performance. It results from engine tests. New classes will be added when new requirements appear from builders. The first letter indicates the area of ​​use: S - gasoline engines. C - Diesel engines. The second letter indicates the quality: A to J: SJ corresponds to the maximum quality currently for gasoline engines.

C to F: CF corresponds to the maximum quality currently for diesel engines. The API awards an "energy saving" label when the fuel consumption gain is 0.5 to 1.4% depending on the grade, compared to a 5W30 synthetic oil serving as a reference.

5 / What are the best oils?

The best oils are those that are quite simply suitable for your vehicle. To find out which ones, we must refer to what the car manufacturers recommend. However, for the most demanding, there are high performance oils that exceed the manufacturer's standards, but it is more valid for performance cars, for the average user, the recommended oils are more than sufficient.


6 / How often should I change my oil?

The frequency of oil changes varies depending on several parameters: the type of oil, the mileage of the vehicle, the type of engine use (race, city, highway, etc.), the time between oil changes.

- However we can define reference thresholds for oil changes not to be exceeded, the wear check is to be done by the mechanic or by yourself if you have the knowledge to see if it is not necessary to advance the time of the oil change.

- A 5w30 or 5w40 oil allows longer oil change intervals: spaced from 20,000 to 30,000 km for the latest generation diesels (type DCI, HDI, TDI for example). And from 10 to 15,000 km for the essences.

- Even if you have not reached the prescribed mileage, you should change the oil at least once every 6 months.


7 / Which oil to choose?

- For regular use at low temperatures such as Canada, we recommend the use of a low viscosity index oil allowing optimal lubrication of the engine (eg: 0W-20).

- For regular use at moderate or hot temperatures as in Algeria, we recommend the use of a high viscosity index oil allowing optimal engine lubrication (eg 5W-40).

- For competition use, we recommend the use of an oil with a high viscosity index allowing optimal lubrication of the engine at high temperature (eg 10w-60).

- If you have an "old" petrol vehicle from before 2000, a diesel without turbo and / or high mileage, 15w-40 oil. Being thicker, a 15w40 can compensate for high oil consumption. It is advisable with this viscosity to reduce the oil change intervals because this type of oil loses its lubricating properties more quickly.

- If you have a "recent" engine after 2000 (whether diesel or gasoline) with low mileage, the 5w30 or 5w40 are recommended.

- If you have a vehicle equipped with a particle filter, it will be 5w30 (standard C1, 2, 3, 4 ... depending on the make of the vehicle).



8 / Where to do my oil change?

You can at any independent garage or authorized agent or yourself if you have the skills and equipment for, however, do not forget to drop off your used oil at authorized deposit points.

Please note that some dealers in Algeria oblige to change the oil in their network so as not to lose the warranty.



9/ Expiry date


So, is there an expiration date on the oil? No. But the shelf life varies according to the use that has been made (or not) of the container. If the container has been opened, then it is advisable to use the oil within a year of opening it.


Things get more complicated for cans that have never been started. But there is one certainty: an oil that has not been opened can be stored for a long time. Several years even.


But this number of years varies according to the brands and there is not an “official” figure. Generally speaking, manufacturers guarantee the viability of their oil for a period ranging from 3 to 5 years, depending on the brand.


In short, this does not mean that the oil will necessarily be unusable after 3-5 years. But beyond this period, oil companies no longer guarantee anything. So at your own risk...