The fluidyne, or liquid-piston Stirling engine, which incorporates liquid columns as displacers/pistons in a heat engine to convert low-grade heat into useful work, is discussed. The advantages of this type of machine include potential for low cost, low maintenance, reliability, and self-starting capability. These factors are typically offset by poor thermal efficiency and low specific power. Experiments designed to differentiate between possible models of displacer excitation are described. The results point to possible improvements of tuning line design. >