Posted 7/12/2020 17:00 (#8369663 - in reply to #8369279) Subject: RE: another steam locomotive question,
NEMO
Like a diesel engine black smoke usually means unburned fuel. My guess is that the one puffing steam out was the one under the most pull and the other was being a slacker.
It's not uncommon for a steam engine to smoke excessively until it reaches optimal operating temperature and is put under a heavy load.
Also some engines where just more efficient than others.