Abstract: The invention relates to a method, and to an engine for applying the method, for testing different substances, such as lubrication substances, cooling substances and/or fuels or the like, in a combustion engine, especially in a big diesel engine, which comprises at least two, preferably several cylinders. According to the invention at least for the part of one cylinder the supply and circulation of at least one substance is arranged separately and sealed from the corresponding substance systems for the other cylinders of the engine, and for the part of said cylinder the composition and/or some physical property, for instance temperature, of said substance to be supplied is changed in comparison with the substance to be circulated simultaneously in the corresponding substance system for the other cylinders in the engine.