In conclusion, we successfully constructed a molecular crystal-based thermal engine that can extract kinetic energy from ambient-temperature differences. The flexible conversion of the kinetic energy of the weight to the potential energy of crystal deformation and the rapid deformation of the crystal to accelerate the weight are crucial factors for continuous motion. The bending of the weight-loaded crystal as the temperature decreases correlates with the straininduced phase transition associated with crystal elongation, which occurs preferentially in the outer-arc region. The mechanical properties and energy efficiency of our porphyrin-based system can be modified by changing the alkyl chain length, inserting metals, and constructing solid solutions.