Abstract: A thermal hydraulic engine including a frame. A working fluid changes volume with changes in temperature. A working fluid container houses the working fluid. A cylinder secured to the frame includes an interior space. The cylinder also includes a passage for introducing the working fluid into the interior space. A piston is housed within the interior space of the cylinder. The working fluid container, the interior space of the cylinder, the piston, and the working fluid container define a closed space filled by the working fluid. The engine also includes means for transmitting heat to and removing heat from the working fluid, thereby alternately causing the working fluid to expand and contract without undergoing a phase change. The piston moves in response to the expansion and contraction of the working fluid.