Oil check

The life of an engine oil is determined by many factors: the mileage of the vehicle, the quality of the oil itself, and the season and conditions under which the vehicle is operated. The winter period, the city cycle, heavy loads and frequent unsuccessful engine starts adversely affect the condition of the oil. The need for an oil change is determined by many indicators: viscosity change, alkalinity, flash point reduction, contaminant content (water, fuel) and insoluble impurities, the value of dispersing properties. Critical values of indicators for reference are given in the table below.



It should be noted that most of the rejection indicators of oil life can only be determined in laboratory conditions, however, parameters such as the change in oil viscosity and the value of dispersing properties (DC), are available even to a simple car enthusiast.

With a change in viscosity, everything is simple: if the oil becomes too thin during operation (drips off the dipstick like water when checking the level), it is obvious that its physical properties have changed and it is not able to fully perform its functions.


To determine the DS, the oil spot method is used, which is as follows:

• Immediately after stopping the engine, remove the dipstick and wipe it twice to make sure that any condensate is completely removed from the surface of the dipstick Insert the dipstick back until it stops and remove it again, then place a drop of oil from the dipstick on filter paper («blotter») or coffee filter (filter used for coffee makers).
• Lay the paper or coffee filter on a flat, horizontal surface so that the oil stain is evenly distributed over the test material. After 30 minutes, you can judge the condition of the engine oil.

Distinguish the central nucleus (d), corresponding to the spread of oil, and the zone (D) diffusion of oil-insoluble pollution products around the central core.

A decrease in the width of the diffusion zone indicates the operation of additives or the presence of water in the oil. DS oils are determined by the formula:



The value of DS less than 0.3 arb. is considered unsatisfactory. unit, in this case, an oil change is necessary.


Example



In this example, the diameter of the central region (d) is 18 mm, and the diameter of the outer region (D) - 41 mm.

Substituting these values into the formula, we get: DS = 1 - (18²/41²) = 1 - (324/1681) = 1 - 0,19 = 0,81.

The value obtained corresponds to the permissible range from 0.3 to 1. Therefore, the condition of the oil is quite satisfactory.