You might try 4 to 6 drops to start with.  A locomotive's instruction sheet or booklet should tell you for sure.  If you don't have instructions, you might be able to do a web search and find some.

When the smoke output drops off, that's a good indicator that you need to add more drops.

if a few drops helps smoke out put then I would add 10 to fifteen drops if not take apart and check wick sometimes if you have ran it dry you need to replace the wick as it burns or blackens the wick and does not produce very good smoke output!

When I can see across the room, that's when!

I start out with about 0.25 ml using a small needle syringe. You can get syringes at your local farm store in the animal stuff department...or on line. The bird dropper that Lionel sends with the Legacy engines is a bit coarse for a quarter of an ml, but it can also be used if you fill it up about 2/3 of the way to the 0.5 ml line. That is enough fluid to run at least 10 minutes or so. I don't run smoke very long, and when I get an engine out after a month or so, I go ahead and put in the 0.25 ml. I never have seen anything I have get overfilled. I like a measuring device better than anonymous drop sizes.  

There is no universal number of drops for smoke units. The capacity varies widely, from as few as four drops to as high as 30 drops. So refer to your manuals for particular locomotives.

Most locomotives require 10 to 20 drops after they are initially primed, but, again, you can drown a smoke unit for a locomotive designed to take only four to six drops at a time.

I got these Measured Marked Dropper Top for 60ml 2oz Ounce Boston Round Bottles10 Pack on Amazon for use with the Mega Steam smoke fluid I use. It has really helped me from overfilling!

Fan driven smoke units won't work at all with six drops, so it's important to specify specifically what locomotive and type of smoke unit you're dealing with.

gunrunnerjohn posted:

Fan driven smoke units won't work at all with six drops, so it's important to specify specifically what locomotive and type of smoke unit you're dealing with.

The engine is Pennsylvania Lines West Legacy H10 7109 SKU: 6-85386

smoke unit fan driven 

One full dropper at the end of each operating session.

Jon

PRR_railfan posted:

gunrunnerjohn posted:

Fan driven smoke units won't work at all with six drops, so it's important to specify specifically what locomotive and type of smoke unit you're dealing with.

The engine is Pennsylvania Lines West Legacy H10 7109 SKU: 6-85386

smoke unit fan driven 

 

I have one of these and had the smoke unit apart to lube the fan. The reservior will easily handle 20 drops. i believe the manual calls for 20 on the first fill and 10 there after.

Smoke production will drop off substantially if your low on fluid as the thermistor will cut power to the element.  

Having said that, the thermistor does a nice job of extending the life of the wicking by greatly reducing the charring.

The whistle steam will go much longer on a fill than the stack unless your laying on the whistle the entire time.

Good to add some at the end of running, and then depending on how long its been add some at the start.  Adding a lot before use tends to cause spitting of the fluid in liquid form, whereas adding at the end of running allows ample time for the fluid to get absorbed by the wick.  

Amount of fluid to use varies greatly. My 6-28009 Santa Fe Hudson manual says 4-8 drops. My 6-18588 Alco C420 engine with fan driven smoke manual says 35-40 drops. I stick to the 4-8 in my post war 2020, 2025, and 2065 engines. The 2020 has original pellet unit, the 2025, and 2065 have replacement liquid units. I find putting fluid in at end of the runs works very well for smoke the next day.