CHAPTER 2 - PART 4 - ENGINE AUXILIARY SYSTEMS - LUBRICATION SYSTEM

The lubrication system lubricates the moving parts inside the engine, reducing friction between them. At the same time, it helps cool the components, remove impurities and protect surfaces against wear.

A lack of lubrication or overheating of the oil can lead to engine seizure or severe engine damage.

THE LUBRICATION SYSTEM COMPRISES:

• the oil pump ensures that oil circulates under pressure throughout the lubrication system, so that all parts subject to friction are properly lubricated;

Types of oil pumps: Automotive engine lubrication systems mainly use fixed-displacement gear pumps with internal or external gearing. Other designs include eccentric pumps or piston pumps, although these are less common in modern automobile lubrication systems.

The oil pump is driven by the crankshaft or the camshaft.

• the pressure relief valve: maintains oil pressure within the limits specified by the manufacturer, with typical values of approximately 2-5 bar, depending on the engine type. When the pressure exceeds the maximum limit, the valve opens and allows some of the oil to return to the oil sump, preventing excessive pressure from building up in the system;

• the oil filter traps solid impurities and helps remove oxidation products, water and any traces of fuel from the oil;

• the dipstick (oil level indicator) is a metal rod used to check the oil level in the oil sump. The minimum and maximum limits are marked on it. A drop in the oil level may be caused by leaks or by normal or excessive engine oil consumption.

ENGINE OIL

Engine oil is a fluid that forms a lubricating film between moving parts, reducing friction and wear and preventing direct contact between metal surfaces.

The oil level must be checked using the dipstick and maintained between the minimum and maximum marks.

An excessively low level can lead to insufficient lubrication, while an excessively high level can affect engine operation by causing oil foaming and increasing pressure in the system. Therefore, the oil level must be maintained between the minimum and maximum marks on the dipstick.

It is recommended to check the oil level before a longer journey and at least once a month.

Engine oil composition:

• base oil - can be mineral, synthetic or semi-synthetic, with lubrication as its main function;
• additives - chemical substances that improve the oil's properties (protection, stability, cleaning);
• cleaning and dispersing agents - keep impurities in suspension and prevent deposits.

Even if the number of kilometres specified in the technical documentation or service manual has not been reached, the oil must be changed if the time interval set by the manufacturer has been exceeded.

Depending on the type of base oil used, engine oil can be mineral, synthetic or semi-synthetic.

The main characteristics of engine oil are:

• wear protection;
• viscosity in relation to temperature;
• chemical stability.

In general, motor vehicle manufacturers specify the recommended oil type in the vehicle handbook through:

• the SAE viscosity grade (for example: SAE 5W30, 15W40);
• the manufacturer's own specification (for example: VW 505 00, BMW LL-04).

Example: 5W30:

• the number 5 indicates the oil's behaviour at low temperatures; a lower value means better flow when cold;
• the number 30 indicates the oil's viscosity at the engine's operating temperature; this value must be chosen according to the manufacturer's recommendation, rather than on the assumption that a higher number is automatically better.

Following the manufacturer's specifications regarding engine oil type and oil changes helps ensure correct engine operation and extend the engine's service life.