Because the combustion products must transfer their heat to water before the energy can be used, I think there is an inherent limitation on the efficiency of a steam engine as compared to internal combustion.

I was interested in steam cars for a while, I have a manual to a Stanley Steamer and a short book published by Lindsay on them.

However it was reading the history of steam that is in the opening chapters of Lyle Cummin's "Internal Fire" and his description of the limitations of steam and sterling engines, that I came to think there was a fundamental reason behind it.

The Doble and Stanley era cars seem to have gotten about 10 mpg.

On the other hand, they do have a possible advantage in being able to consume a variety of non-standard fuels. There may be a niche market for that, which given the relative size of the car markets in 1925 vs 2015, is quiet huge and could support a sizeable company.