The Minto engine is a liquid piston heat engine that converts heat energy. into mechanical energy. Evaporation of the heated, volatile working fluid pushes it upwards against gravity. This causes the device to tip over and rotate. A 500 mm diameter Minto engine which used petroleum ether as the working fluid, was built and was operated between 344 K and 294 K. Thermal efficiencies of up to 0.25% (i.e. 1.7% of the Carnot maximum) were measured. This engine behaves as a power amplifier. It absorbs low grade heat over a long period of time and suddenly releases it as a pulse of mechanical energy over a short period of time.