Highly effective cleaning fluid for clearing the engine interior of troublesome deposits. Dissolves sludge and lacquer formers quickly and reliably. All types of oil-soluble and oil-insoluble residues are brought into suspension and removed during the next oil change. An engine which has been cleaned of deposits and contamination and which is then filled with fresh oil not contaminated with old impurities can develop its full performance characteristics. Wear in the engine is thus reduced and the service life is extended.