Abstract: Fines, that are present in lubricating oil, and their organo-metallic coatings are contacted with aqueous solutions of strong acids to solve the problems of plugged cartridge type filters. The present process employs a washing step whereby, following a filter cycle that is terminated due to a pressure build-up, a hot aqueous solution of a strong acid with a pH of approximately 1.5, is circulated through the plugged filter cartridges until the fines and organo-metallic coatings are solubilized. The acid wash solution is kept separate from the filter feedstock and filtrate by suitable valving, piping and tankage so as not to contaminate it. The filter cartridges may be rinsed prior to reintroduction of the feed stock to begin the next filter cycle.