Engine Oil

All engines require some form of lubrication and this is provided by the Engine Lubrication System. Engine oil is the main component of this  system. The Engine Lubrication System circulates the Engine Oil through out the Engine to provide lubrication to all the components. This oil is required to carry out numerous tasks when the engine is in operation, the primary function being lubrication all the components. It  reduces friction and prevents metal to metal contact. The Engine Oil stops two  surfaces from touching each other by forming a thin lubricating film  on the mating surfaces.

Constituents Of Engine Oils

The engine oils consist of a base oil and several several other additives.  The base oil may be mineral oil produced by refining petroleum or it may be synthetic oil produced in laboratories. The base oil generally constitutes  70-95% of of the engine oil. The additives at other hand may constitute 5-30% of the engine oil and are responsible for imparting some essential properties to the engine oil. The most commonly used additives are:

1. Viscosity Modifiers

Helps in maintaining the optimum viscosity at different temperatures.

2. Detergents

Helps in cleaning the sludge and scales formed on the engine components. They also neutralises the acidic compounds formed in the engine oil. 

3. Dispersants

They also helps in keeping the engine clean. They help in forming a dispersion or suspension of shoot particles and prevent them from forming agglomerates.

4. Anti Freeze

Prevents the engine oil from freezing and boiling. It decreases the freezing point while increases the boiling point of the engine oil.

5. Oxidation Inhibitors

Engine oils tend to oxidise over the time. This oxidation reduces their lubricating capability.  To prevent them from oxidation the Oxidation Inhibitors are used.

6. Anti  Foaming Agents

The detergents and the continuous flow of engine oil may lead to the formation of foams. These foams may affect the performance of lubricants by increasing their rate of oxidation. Anti Foaming agents control the formation of bubbles by reducing the surface tension of the engine oil.

7. Corrosion Inhibitors

Prevents the corrosion or rusting of the engine compartments

8. Anti Wear Agents

They help in reducing the wear and tear of engine components by forming a layer of oil around them.  They are polar in nature and hence have tendency to stick to the metal surface.

Functions of Engine Oil

The functions of engine oil are as follows-

1.To lubricate the mating surfaces and prevent the wear and tear of engine components.

2. To cool the engine components and hence help in maintaining their optimum temperature.

3.To clean the different components of engine.

4.To act as a seal on mating surfaces of piston rings and the cylinder block and hence prevent the combustion gases from leaking to the crankcase.

Grades Of Engine Oil

Society of Automotive Engineers (SAE) has developed numerical coding system to grade the engine oils according to their viscosity. SAE viscosity index includes the following numbers: 0, 5, 10, 15, 20, 25, 30, 40, 50 and 60. Lower numbers means lower viscosity and a higher number means a higher viscosity.

Monograde Engine Oil

These oils are not able to maintain optimum viscosity if their temperature changes. They work well only when their temperature is steady. Mono-grade oils become thin as they get heated and become thick as they cool down. Also, a mono-grade oil does not use any additive or viscosity modifier.

Multi Grade Engine Oil

These oils are suitable for use over a wide temperature range. They are also called All season oils.  Their viscosity do not change abruptly due to temperature change and remain in an optimum range. They are neither very viscous at low temperature nor very thin at higher temperature.

Why Do We Need Multi Grade Oils?

The engine oil has to encounter different temperature conditions as the engine operates. When the vehicle is parked  or during winters, its temperature falls to a very low level. During running condition the engine produces huge amount of heat. This heat is carried away by the engine oil, increasing its temperature.  At low temperatures the engine oil remains thick and viscous.  When heated it becomes thinner. 

During winters or generally at the time of starting, the oil remain cool. At low temperature the viscosity of the oil decreases making it highly viscous. The highly viscous oil do not flow easily. It is also very difficult to pump it, all along the engine. It puts huge load on pump and may also cause oil filters to choked. At the time of starting, the engine oil need to be pumped quickly to all the components. This is not possible with highly viscous oil. Hence, at low temperatures the engine oil need to maintain a lower viscosity.

At higher temperatures the viscosity of the oil decreases and it becomes thinner. If the the viscosity drops below the optimum levels, the chances are high that thin oil layer can not prevent metal to metal contact. This may increase the rate of wear and tear of engine components. So, at higher temperatures the engine oil must have sufficient viscosity to form a thick lubricating layer around the components.

To cater to these requirements we need an engine oil which neither become too viscous at low temperatures nor becomes too thin at high temperatures. This problem is solved by multi grade engine oils. These oils contain different additives which helps them in  maintaining optimum viscosity at all operating temperatures. These additives are polymeric compounds called viscosity modifiers.

Naming of engine oil

5W30 oil

The name of engine oil contain some alphabets and some digits. You might notice names as 10W-40 or 5W-50 etc. Here 'W' means that the oil can be used in winter also. Or either it is an all weather oil. The first digit represent the viscosity at low temperature ie. Around 0 degree Fahrenheit. Lower the number, thinner the oil at low temperatures.  The second digit represents viscosity at 100 degree Celsius. Higher the number, thicker the oil remains at high temperatures. For example the oil 10w40 remain more viscous than 5w30  at 100 degree Celsius.

These were some basic information regarding engine oil. Looking at the importance of engine oil we must always use the quality oil specified by the automobile companies. Always use the recommended grade of engine oil so as to improve the performance of your vehicle.All engines require some form of lubrication and this is provided by the engine oil. This oil is required to carry out numerous different tasks when the engine is in operation, the primary function is to lubricate all the components by reducing friction and preventing or reducing metal to metal contact. The oil stops two  surfaces from touching each other by forming a thin lubricating layer on mating