The results of the study of the thermo-oxidative stability of Castrol Magnatec R 10W-40 SL/CF partially synthetic engine oil with cyclic test temperature changes from 150 to 180 °C and from 180 to 150 °C taking into account the thermal energy absorbed by the products of oxidation and evaporation are presented. The graphical dependences of the decimal logarithm of the thermal energy absorbed by thermostatic products on the decimal logarithm of the test time are obtained, which are described by linear equations in the cycles of increasing and lowering the test temperature, which made it possible to determine the effect of time on the indicators of thermo-oxidative stability.

During the running motor oil quality determination oil makeup has a big influence on thermal oxidation mechanism, however there is a problem of insufficient examination of makeup influence on motor oil conditions. Main goal of these researches is to determine how makeup effects on motor oil’s thermal oxidation stability. For the research Lube oil Lukoil Super 10W - 40 SG/CD has been chosen. Thermal oxidation stability results assessment was conducted basing on obtained values of: light stream absorption criteria, volatility and thermal oxidation stability criteria in cases of research with makeup and without it. There was offered a criteria of makeup influence on thermal oxidation stability values, which identified as change of light stream absorption rate proportion and thermal oxidation stability criteria in case of research with and without makeup. Research methodology involved motor oil test on thermostating device consequently under temperatures 180, 170 and 160 °C with makeup and without it in condition when quantity of makeup oil corresponded to vaporized oil quantity. Research results demonstrated that oil makeup decrease thermal oxidation intensity on the whole temperature test rate.

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The object of research is influence of temperature and destruction products on boundary layers formation located on rubbing parts. There are research results of anti-wear properties of mineral and partially synthetic motor oil using methods for determining parameters such as absorption coefficient of the light flux, viscosity, and friction parameters. As result there is analyze of experimental data, absorption curve, that are showing anti-wear properties of lubricants, also proposed criterion that is showing concentration of destruction products on the nominal area of friction contact.

This article presents the results of a study of the effect of temperature tests on indicators of thermal oxidative stability: optical density, evaporation, coefficient of thermal oxidative stability. A grapho-analytical model is proposed for determining these parameters for a wide range of temperatures without temperature control of oils using experimental results obtained at two temperatures. A comparative evaluation of the experimental data with the calculated ones obtained using the grapho-analytical model has been carried out.