A Fluidyne engine is a Stirling engine with liquid pistons that automatically start to oscillate when the engine's regenerator is differentially heated to a certain level. This study investigates the thermally induced oscillations of the working gas and liquid in the Fluidyne engine using the results of the thermoacoustic theory. Further, the water pump performance of the Fluidyne engine is evaluated when it is coupled to the pumping line. The theoretical formulation and calculation results were verified by experimental tests on the onset temperature ratio and pump performance.