A closed cycle vapor engine has evaporator and condensor elements utilizing liquid carrying wick means arranged to provide surfaces for the evaporation and condensation of the engine working fluid and to transport said fluid in liquid form from the condensor to a condensate pump and from the condensate pump to the evaporator. Vapor passages connect the evaporator and condensor with the intake and exhaust openings of the expander, providing a closed system in which the evaporator and condensor operate essentially on the principle of a heat pipe.