Mike, I just saw your post. It great the engine began smoking once again.
The Lionel recommended fill for a dry AF smoke unit is 20 drops. That is based on using their dropper and smoke fluid. On new engines I put in 20 drops, let it sit about 10 minutes and then add 10 more. They smoke great and the smoke units are not overfilled. I always put in 10 drops prior to running any engine that has not been used in the past day.
Lionel, Challenger and JT's Megasteam are all about the same viscosity and work well. The outlier is SuperSmoke. It has a higher viscosity, does not wick into the smoke batting quickly , and can create a lot more residue. I do not use it in the Lionel AF smoke units nor in the MTH units used in the American Models conversions. Also never add it to one of the Seuthe smoke units in the TMCC Mikados and light Pacifics, it will stop smoking. SuperSmoke is fine in the original Gilbert smoke units and the American Models factory smoke units and has the same scent as the original Gilbert capsules.