I just run air. If I am fording a stream I might run water for a bit. I've even used snow before.
Technically I would guess my current coolant of choice is Rotella 15W-40. It never boils over...
Where can I buy that air? Does it come in different grades, or will the 1 air work on anything? Lastly, I'm riding this weekend so I'll need it quick, do you think they can air-mail it to me?