AbstractThe antifriction properties of calcium phenate‐type detergents of different lubricity were investigated by laboratory methods. Simulation of the operating environment in super‐long‐stroke marine diesel engines was achieved using concentrated sulphuric acid. The influence of the tested additives on engine oil antifriction properties was determined after their being mixed with acid. The tribological performance of oil samples with 50 and 70 TBN values was characterised by testing on a friction machine, and by thickness determination of friction surface layers using Auger spectroscopy. It was found that the effectiveness of antifriction action of the detergents tested depends on the thermal stability of the lubricating layers, the temperature at which the destruction of the boundary lubricating layers occurred, and the thickness of secondary structure layers in the metal surface of the friction