More fluid s a good idea but these conventional locos aren't big smokers. The smoke unit voltage is based on how much throttle your giving the loco and how much it is drawing.
The easiest way to improve the output is to add more cars to the train increasing the load on the train thereby causing it to draw more voltage.
You can also put the loco in neutral and raise the throttle this will heat up the unit, but it will likely cool back down once the loco is underway.