Chapter VIII - The lubrication system

The lubrication system supplies all the joints of the engine where there is friction, filters and cools the engine.

The lubrication system consists of:

- the oil pump: performs the circulation under pressure of the oil through the lubrication system, thus ensuring the lubrication of all the parts;

Types of oil pumps:

• with pinions (gears);
• with eccentric;
• with piston.

The drive of the pump can be made from the crankshaft or from the camshaft. The most widespread pumps are those with constant displacement, with gears, with internal or external meshing.

The overpressure valve is adjusted in such a way that the oil pressure is maintained within the limits of 2 to 4 daN/sq cm. When the oil exceeds the maximum limit, the force exerted by the spring on the ball becomes smaller and it opens the return channel of the oil into the sump.

- the oil filter: retains solid impurities and, as far as possible, removes oxidation products, water and fuel;

- the dipstick (the oil indicator): is a rod that indicates the oil level in the sump. At the end of the rod there is a mark that indicates the minimum and the maximum level of the oil in the oil sump. The low oil level in the oil sump can be due to oil leaks or excessive oil consumption by the engine. The high oil level can be due to water entering the oil sump.

Engine oil

Engine oil is a fluid that has the role of creating an insulating film between the various moving elements inside the engine.

Checking the oil level in the oil sump is done with the help of the dipstick on which two marks are inscribed: maximum and minimum. The correct oil level in the sump must be between the maximum and minimum marks.

It is recommended that the oil level in the sump be checked before a long trip and at least once a month.

Engine oils consist of 3 elements:

• base oils, which can be mineral, synthetic or a combination of the two, and their main function is the lubrication of the lubrication system;
• additives - these are chemical substances which, combined with the base oil, have the role of improving certain characteristics of the oils used in the lubrication systems of thermal engines;
• detergents or dispersing agents.

Engine oil loses its properties due to wear as a result of use, but also due to degradation over time.

Even if the number of kilometres specified in the service manual is not reached, but the time interval is exceeded (the oil expires), it must be replaced. Once the oil is replaced, the oil filter will also be replaced.

From the point of view of its chemical composition, it is mineral, synthetic or semi-synthetic.

The main properties of engine oil are:

• resistance to wear;
• viscosity depending on temperature;
• chemical composition.

In general, the information specified by vehicle manufacturers in the vehicle manual regarding the type of oil used is:

• the SAE viscosity grade (Ex: SAE 5W30, 15W40);
• the vehicle manufacturer's standard (Ex: VW 505 00, BMW LL04). For example: 5W30;
• 5 represents the cold viscosity, the lower it is, the better the oil is;
• 30 represents the hot viscosity, the higher this figure is, the better the oil is.