Cleaning fluid for clearing the engine interior of troublesome deposits. Dissolves sludge and lacquer formers. 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. Flushes out and cleans the oil circuits of motorcycles with four-stroke gasoline engines. The frequency of use is dependent on the degree of contamination of the oil circuit and on the quality of the oil used.