I have a clear recollection of Bill Lear, famous for the Motorola Radio company, Lear Jets, and many
other innovations and businesses, designing and building into a GMC Fishbowl transit bus a prototype
demonstration engine/boiler/drive-line/working fluid substitute he called "Learsium(?)" (of course he did).
The basic idea was to completely seal the system so the used Steam(learsium) was captured and recycled
after use and not vented overboard like in most steam applications. I saw a publicity picture of the thing
in some publication years ago and always wondered how it turned out. This was in the 70's 80's or
thereabouts. The idea was a good concept so you don't have the issue with always needing water for the used steam, and the learsium was a very special and secret formula never revealed of course. I guess it didn't work out so well since nobody even remembers the attempt today. But he did build the demonstrator and it did drive around for testing. But not for very long, it was finally abandoned.