I couldn't find any of them by searching with the word 'steam'. that is why I added it. Do you want me to remove the extra info?

edit:

I see my mistake. Steam cars are not listed as steam engines so you have to do two searches to find all steam powered vehicles - one for steam engine (category) for tractors/rollers and one for steamer in extra info for cars.

edit:

I have removed the extra info I put in. I did notice that there is inconsistency in the class for these things. Some are listed as construction equipment and some are listed as steam engines for the same type steam tractor. I guess there is confusion because both are correct but you can only select one.

There was already a "steam" category though:
http://www.imcdb.org/vehicles.php?resultsStyle=asImages&makeMatch=2&make=&modelMatch=- 1&model=&modelInclModel=on&modelInclChassis=on&class111=111

FYI: I added the word 'steam' in the extra info for all the steam vehicles I could find so that a search could find them by category. I probably missed some and just wanted to make you aware of what I did.