Ticking (or unticking if it was already set) the refuel checkbox isn't being saved when you close the window. Therefore you can't set new trains to automatically refuel.

I think this broke somewhere in between 0.16.18 and 0.16.22.

This looks very similar to the earlier 0.16 bug reported on the earlier 0.16-version of this mod : https://mods.factorio.com/mod/SmartTrains-016/discussion/5a5f1b0dadcc441024d7735c

I've found a small workaround for toggling the refuel checkbox:

1)Click on refuel to toggle it ON
2)Without clicking anywhere else, press enter to toggle it OFF again
3)Exit the train gui. When you reopen it, the refuel checkbox should be ON.

Worked every time for me.

i cant figure out how the refueling works any help?

THANK YOU Faultzone! Your workaround works, that little bug was driving me crazy. BTW, you can also save the schedule as a line and the checkbox to have that line refuel works normally. Just slightly annoying for me to do that for every train :p

To MetalSkinGaming, just make a station and change its name to "Refuel". Trains with that setting enabled will go there when they are low on fuel, so set up some inserters to insert whatever fuel you are using into the spaces where the locomotives will stop at.

Should be fixed now. Sorry for the long wait