An exhaust system configured for converting thermal energy to mechanical energy includes a source of thermal energy provided by a temperature difference between a heat source having a first temperature and a coolant having a second temperature that is lower than the first temperature. The cooling system includes a cooling circuit configured for conveying the coolant to and from the heat source. The cooling circuit includes a conduit and a pump in fluid communication with the conduit and configured for delivering the coolant to the heat source. The cooling system also includes a heat engine disposed in thermal relationship with the conduit and configured for converting thermal to mechanical energy. The heat engine includes a first element formed from a first shape memory alloy having a crystallographic phase changeable between austenite and martensite at a first transformation temperature in response to the temperature difference between the heat source and coolant.