Abstract: High antiwear properties and flatness of the viscosity-temperature characteristic are one of the main requirements for engine oils, which depend on the viscosity of the lubricant. The viscosity of engine oils is greatly influenced by temperature. Also, the viscosity depends on the hydrocarbon composition and the depth of purification of oil fractions, the presence of viscous additives and the volume of new oil filling-up to the total volume of lubricant in the engine lubrication system. The need for oil filling-up is explained by decrease in engine oil level due to its waste and leaks in the engine lubrication system. However, the influence degree of oil filling-up on engine oils viscosity of has not been studied enough. Thus, the purpose of this research was to determine the filling-up influence on the kinematic viscosity of mineral (M-10G2K, Lukoil Standard 10w-40 SF/CC), semi-synthetic (Lukoil Super 10w-40 SG / CD) and synthetic (Castrol Magnatec 5w-40 SL/CF, Lukoil Synthetic 5w-40 SL/CF, Mannol Elite 5w-40 SL/CF) engine oils during their oxidation. The research methodology included testing a sample of engine oil on a device for thermal oxidation in two stages: without filling-up and with filling-up of new oil. Every 8 hours of testing, the mass of the evaporated oil was recorded and instruments readings were taken from photometric device and low-volume viscometer. In the case of the filling-up test, the sample was filled with new oil to its original weight before each subsequent eight-hour test. Research results of oil filling-up influence on the kinematic viscosity of various bases engine oils, that were tested in the temperature range from 160 to 180 ° С. A method for monitoring the viscosity properties of a lubricant has been proposed, which makes it possible to quantify the change in the kinematic viscosity of the oil as a result of its oxidation and under the influence of oil filling-up. It was found that the degree of oil filling-up influence on the kinematic viscosity depends on the test temperature and the nature of the lubricant base.
Index terms: kinematic viscosity, density viscosity coefficient, thermal oxidation stability of engine oil, light stream absorption coefficient, oil filling-up.


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