Morgans wrote:
"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?

No, it's not that.

Fuser oil was used in older copy machines.
It's a clear, probably silicon-based oil
that kept the fuser rolls soft and pliable.

Haven't seen it for years.