GL stands for gear and lubricant. 1,4 and 4 shows the level of performance according to the gear type. For example, GL-1 is a mineral-based gear oil for spur gears. GL-5, on the other hand, indicates that it can be used in Hypoid type gears and its level.

W is the initial of the word winter and indicates that the oil is suitable for winter conditions. 0 and 5 indicate the viscosity grade of the oil.

The performance level of every oil should be written on the packaging and labels. Performance values are determined by organizations such as API and ACEA. According to API classification, S indicates gasoline engine oil, C indicates diesel engine oil, and S/C indicates that that oil can be used in both gasoline and diesel engines. The letter next to S and C indicates which year the oil is at the top performance level suitable for the engine technology. For example, SL: indicates the top performance level of 2001 in the gasoline class, CI-4 indicates the top performance level of 2002 in the diesel class.

Synthetic oils are oils obtained by special chemical processes. Mineral oils are natural oils obtained by refining petroleum. It is not recommended to mix the two kinds together.

Although there are applications made with observation in practice, in order to understand that a motor oil deteriorates and loses its function, it needs to be tested extensively in the laboratory.

The darkening of the oil does not mean that the oil has deteriorated. One of the functions of engine oil is to keep the engine clean. Thanks to the detergent-dispersant additives the oil contains, it cleans the soot and pollution and absorbs it into its body. As a result, its color darkens. This shows that the oil is doing its job.

The decrease in the oil level due to the burning of the oil entering the combustion chamber through the opening between the piston ring and piston is a sign of depletion. The reasons are:

  1. Failure to use oil with appropriate viscosity,
  2. Burning of oil by escaping into the combustion chamber due to wear in the engine,
  3. As a result of the continuous use of the engine at high speed, the viscosity decreases with the effect of heat and it burns by escaping into the combustion chamber,
  4. Decreases in tolerance from the design of the motor.

Attention should be paid to the temperature of the engine. Emptying and filling should be done while the vehicle is on level ground. It must be ensured that the old oil has completely drained from the engine crankcase. It should not be forgotten that the sump plug is re-sealed when the process is finished.

The resistance of fluids to flow is called viscosity. Its unit is stock in the CGS unit system, and in practice centi stock (cSt) with !/100 is used. It is a parameter that should be considered at every stage of lubrication.

The process performed to reduce friction and facilitate movement by forming a film layer on two working metal surfaces is called lubrication. The liquid and solid substances used for this purpose are called oil.

Normally, the engine manufacturers determine the oil change period in engines. Synthetic oils are more durable than mineral oils. Therefore, the oil life is longer than mineral oils. The prolongation or reduction of the maintanance period is closely related to the conditions of use and fuel quality, especially in diesel engines.


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