mythbusters were able to show a weird effect where the fan on a boat thing worked - I think they chalked it up to some blown wind from the fan drawing in more than from around the fan..
From a physics point of view it's not like they created an infinite motion machine, the stored energy in the liquid petroleum is being burned, heat from the internal combustion engine radiated into the atmosphere, etc.
It's just converting stored energy (some amount of kJ or kWh in a fuel tank, or battery) into an aerodynamically weird highly inefficient thrust method.
https://youtu.be/uKXMTzMQWjo?t=75