Steve Grosekemper wrote:Kris,
The stuff in the can will last only marginally longer than the stuff in the car as the master cylinder reservoir is open to moisture and the can is only exposed to the moisture that entered when you opened it...
Being a thrifty Scot by heritage, I always save the leftover 1/4-can (tightly capped) in my trailer, for emergency topping off of the master cylinder reservoir in the future. If you have to do a quick bleeding at the track because of fade, you usually don't need to do another full flush, you just need to pump out the few bubbles that have accumulated in the caliper, so having a small amount of replacement fluid to top off can be useful. It will still be fresher than what is in the system, and you won't have to open a new can just to bring the reservoir back up to full.
If I haven't used the leftovers by the next time I flush the brake system, it gets disposed of with the dirty fluid and the next can takes its place. Since going to 930 brakes on my early car, with good cooling, I have never once had to do any emergency bleeding at the track again, but my old habits persist.
TT