The 3rd Edtion
Gamemaster Companion section about sailing gives a description of the fire engine itself but basically it describes this:
http://www.islandnet.com/~westisle/Hist ... izeng.html
I would therefore expect it to be about as noisy and steamy as a Mississippi paddle-wheeler. As for 'real' smoke, I'm not sure. Since, from my understanding, it is not burning 'real' fuel but instead using True Fire it might or might not be 'polluting'. I don't know if there is a clear description of the effect of True Fire combustion effect on the air surrounding it anywhere in the books.
As for the other questions concerning size and and signs of a defective engine; I'd expect it to be, again, about the same at those old paddle-wheeler; probably a bit bigger and bulkier. The components of the engines would all be made by hand and probably heavily decorated with metal carvings. I would expect the engine general appearance to be varying from Aropagoi to Aropagoi and, on a lesser degree, from Niall to Niall.
Personally, I find it odd that the other races are unable to re-creates fire engines no matter 'divine intervention'. For a society with the level of technology like Barsaive, the only 2 problems with steam engines would be:
A- Actually having the idea of using steam as a source propulsion.
and, most importantly,
B- The existence of steel, since even the strongest iron would not be able to withstand the pressure of a engine powerful enough to power a riverboat.
Since the knowledge of the engine itself and its general concept is widely known, 'A' is not an issue anymore. As for 'B', Earthdawn is, historically, a few thousand years before the invention of steel but they are, in fact, producing weapon grade steel on an everyday basis (lost knowledge at the end of the 4th Age like so many other things?) so that's not an issue either.
I could imagine Upendal somehow preventing True Fire working with other race's copies of the fire engine but they could easily just use 'regular' fire with wood as fuel (I kinda remember reading in a book somewhere that they even had coal I think?) and make it work; less efficient than True Fire true but still working.