smoke fluid

Depends on what you mean by "ok".

There are umpteen threads on this Forum with varied opinions about which brand works best and why and you should search them out.

Also, if the engine is still under warranty, you should review those terms if you decide to switch to another brand. 

@kranky posted:

is it ok to use other brands of smoke fluid in legacy engines?sorry for these rookie questions

As noted above, all brands are pretty much interchangeable BUT Lionel has in the past said if you do not use their premium smoke fluid they will possibly charge you for a repair if it is smoke unit related and you have used another brand.  Personally I like the Lionel and continue to use it after the warranty period but have also used Mega Steam.  Again after the warranty period just so they don't have an excuse.

I have used MegaSteam in my Legacy engines and have sent engines in to Lionel under warranty; never got challenged.

I am known on the forum as the destructor of smoke units till I finally learned how much fluid to add; I either drowned them or starved them; now I have been experimenting with 1 drop per minute of run time - refill after 10-15 minutes of run time and 10-15 drops.  On my new EM-1, I added about 70 drops after a week of running with minimal smoke on time.  My objective is to not burn the wick; watching for a waning smoke stream did not work for me.  Rebuilding a smoke unit is not hard and have rebuilt 2 so far myself; Lionel has parts.

I have been using Lionel fluid for the past few years but will begin using MS (I have a bunch of it) when my Lionel fluid runs low.

You may also be interested in these videos by Laidoffsick:

https://www.youtube.com/watch?v=WRcpFRtA6IY

https://www.youtube.com/watch?v=1asUWbJtfok