Sulfur compounds are formed during the oxidation of motor oil under the influence of high temperatures, and it is quite difficult to determine the residual content of an active additive. To determine the DF-11 additive the M-10G2k oil was oxidized in a thermostat. It was established that with oxidation times of 8 and 10 hours it is only possible to determine the amount of mercaptan sulfur from the potentiometric titration curve. An algorithm and some methods of determination that make it possible to predict the wear and service life of lubricating oil are proposed for complete determination of sulfur-containing compounds in oxidized oil under working conditions.