Checking the oil (Mazda CX-5KE)

The service life of motor oil is determined by many factors: the mileage of the car, the quality of the oil itself, the time of year and the conditions under which the car is operated. Winter, urban cycle, heavy loads and frequent unsuccessful engine starts have a detrimental effect on the condition of the oil. The need to change the oil is determined by many indicators: change in viscosity, alkalinity, decrease in flash point, content of pollutants (water, fuel) and insoluble impurities, the value of dispersing properties. The critical values of these indicators are given in the table below for reference.



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

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



To determine de, the oil stain method is used, which consists of the following:

• Immediately after stopping the engine, remove the dipstick and wipe it twice to ensure that any condensation has been completely removed from the dipstick surface. 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 a coffee filter (filter used for coffee makers).
• Place 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.

A distinction is made between the central core (d), corresponding to the spread of oil, and the zone (D) of diffusion of oil-insoluble contamination products around the central core.

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



A value of de less than 0.3 conventional sd is considered unsatisfactory; 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) is 41 mm.

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

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