The inner abrasive wear characteristics of internal combustion engines were studied. The effect of silica particles and their size distribution on wear was investigated, and oil filters were designed to remove the most harmful particles of 10-20 mu m sizes from the lubricating oil. The improved oil filters were tested under laboratory and field conditions. As a consequence of improved oil filtration thus achieved it was possible to extend considerably the oil-change interval. Transport companies in Hungary have, in a number of cases, adopted the improved oil filters, designated the CF type.