Wear of cylinder liners in fast diesel engines for passenger cars and light commercial vehicles and two wear test methods currently in use are considered. The cold test (engine running at 700 constant RPM, at no load with temperatures of 35° C Max. for oil, 25° C Max for water and 30° C Max. for air) is to be preferred and to be taken as a starting point for an experimental research. The paper critically considers the current opinions on the type of cast iron and its structure which are presently regarded as the best one. To this end two groups of tests have been made to determine the influence of graphite on structure from both a qualitative viewpoint, the importance of certain metallic intercrystalline compounds and their actual contribution in terms of wear resistance.