Preoiler
 

I've recently seen photos of a P51 cockpit which shows a "preoiler" switch.
I understand what it does, question is when (every start, or after long layovers?) and how was it used on this and other engines.

Not a standard feature but an after market add on

Oilamatic Inc. Aircraft Engine Preoiler and Lubrication Systems

Not exactly a pre-oiler, but I once worked a shipboard application of a gas turbine where it was used for "dash" propulsion (a small % of time) - and diesels drove the ship most of the time. During diesel ops, a clutch was supposed to disengage the turbine.

But the clutch was usually dragging, so the turbine would slowly turn for days on end. To protect its bearings, a small electric oil pump was added to keep a small flow going. :D