We have obtained and discussed amplitude and phase frequency characteristics of a normally running engine and taking into account possible malfunctions in the engine based on a series of experiments using filter elements working in the lubrication system for different periods of time. Approximation of the initial schedules has been carried out by the sine sum method. We have offered an algorithm for performing diagnostics and assessment of the filter’s and the engine’s health. Including filter models in the form of transfer functions into the engine’s control system allows to change the lubrication system parameters, improving the engine’s efficiency.