"RST Engineering" wrote in message

Yeah, I did this whole "what fluid to use" thing about four years ago on
this same newsgroup. No, kerosene isn't the optimum choice, but that's
what Lindy had to use going across the Big Pond, and the FAA has proceeded
little from that point.

Mineral oil freezes at a fairly high temperature. Damned few sailboats
out on the water when it freezes, so that isn't a problem for them. It is
for us.

The viscous fluid of choice for compasses is copy machine fuser oil. Good
from boiling to freezing and well past. Thick enough not to ooze past
slightly dried out seals. Not to be used except in experimental aircraft
and aviation quality (ahem) "boat" compasses.

Interesting.

Is that "fuser oil" the stuff that was used in the old purple letter
mimeograph copy machines, or something in newer machines that I know
absolutely nothing about?

I always used to love that smell, of freshly run copies. So if I smelled
that wonderful smell in flight, I know my compass just sprung a leak!

What do the new compasses (those that still have magnets in them) use for
fluid?
--
Jim in NC