Bearing shell idea.

[DevonPaul]

From https://en.wikipedia.org/wiki/LNER_Class_A4
"At the end of Mallard's record run, the middle big end (part of the motion for the inside cylinder) ran hot (indicated by the bursting of a heat-sensitive "stink bomb" placed in the bearing for warning purposes), the bearing metal had melted and the locomotive had to stop at Peterborough rather than continue to London"

Turns out they used to place capsules of Aniseed oil in the bearing shells, so if they started to wear out you would smell it and get an early warning of pending failure.

Simple, yet genius.

 

[mmm-five]

Would we even be able to smell it over the smell of our farts though?

 

[buzyg]

Such a cool tick and a pending trivia question.

 

[MrPT]

Would we even be able to smell it over the smell of our farts though?

Mine smell of aniseed, so it would be impossible to try this without dietary changes.