They were a success! 1806:
Francois Isaac de Rivaz (born in Paris, December 19, 1752; Died in Sion, July 30, 1828) was a Swiss inventor, credited with inventing and constructing the first successful internal combustion engine in 1806. The engine was powered by a mixture of hydrogen and oxygen. The hydrogen gas was contained in a balloon and the ignition was an electrical Volta starter. A year later, Francois Isaac de Rivaz built one of the first automobiles – of course, powered by his new engine.
NOTE: Gasoline was not used for internal combustion engines until 1870.
https://fuel-efficient-vehicles.org/energy-news/?page_id=819
Video of a water powered car from 1974 https://www.bitchute.com/video/VTbTVVWbwMuq/
I hate to be a party pooper, but that claim is so huge it would be equally plausible to say it runs on magical unicorn farts... He was likely mistaken about where the energy was coming from or deliberately lying for some reason. Possibly to hide the real mechanism?
Don't be. Unicorn farts might be an easier sell than the truth of it. Fewer health risks as well. That said, Stan's engine wasn't burning anything...not even imaginary stuff. No oxidation. No chemical reaction. Most of his effort was smoke and mirrors to hide his discovery/invention. There were a few clues. In the end,...rest in peace Stanley.