The invention relates to a motor assembly (12) for a motor vehicle, comprising an internal combustion engine (58) that has an exhaust gas purification device (56) and a heat engine (10). The heat engine (10) comprises at least one closed working space (14, 20) that is filled with a gas. A first cylinder (16), in which a first piston (26) is movably mounted in the longitudinal direction (L) between an initial position and an expansion position, and a second cylinder (22), in which a second piston (28) is movably mounted in the longitudinal direction (L) between an initial position and an expansion position, and at least one heating unit (36, 38) for heating the gas in at least one heating region (40, 42) of the working space (14, 20) and at least one cooling unit (30) for cooling the gas in at least one cooling region (32, 34) of the working space (14, 20) are provided. The gas heated in the heating region (40, 42) pushes the first piston (26) from an initial position into an expansion position, and then flows through the overflow line (18, 24) into the cooling region (32, 34) and pushes the second piston (28) into the expansion position. The overflow line (18, 24) leads at least in sections through the exhaust gas purification device (56).