Abstract: A two stroke steam-to-vacuum engine comprises a plurality of cylinders (500, 502) each cylinder having a piston (504, 510), a piston rod (506, 512), and a steam chamber (508, 514), the piston rods connected for synchronous movement such that each piston is reciprocally moveable between an expanded position and a collapsed position. Admission of steam at 3-5 p.s.i. above atmospheric pressure into the steam chambers (508, 514) is controlled by steam valves (522, 524) and exposure of the steam chambers to a vacuum is controlled by vacuum valves (548, 550). Steam is supplied to the steam chambers (24, 38) through a boiler 520, a solar power source, or an alternative fuel of choice. An auxiliary vacuum tank (572) may be isolated from a primary vacuum tank (554) to replenish the vacuum in a condensate collector tank (560) after removal of condensate.