Brake Fluid Shelf Life Question - And How Much Brake Fluid Needed to Flush Brake Lines

[steve rooney]

This weekend I changed my brake fluid after too many year. 02 Yukon and decided to keep the truck long-term (until she finally dies. Not sure what "finally dies" means). Prior, surfed YouTube and checked out a few posts here to learn how to do. Done and easy. Changing a bunch a fluids as she ages just because they have never been changed.

So my question. I read and heard several places that brake fluid has a shelf life of maybe one year once the bottle has been opened. It made me wonder, if a bottle of brake fluid only has a shelf like of one year then what about brake fluid sitting in the reservoir? How does it not go bad in a short period of time (approx 1-year)? Just wondering. Not a challenge but hopefully you can see why I'm asking.

And a few questions out there about how much brake fluid is needed to flush the lines. It took me just over 32 OZ bottle but you can't really specifically answer the question because it all depends on how much old fluid to new fluid you want to pump through the brake lines. Just putting that out there.

 

[OR VietVet]

Brake fluid will absorb moisture. Sitting on the shelf it will get some moisture to seep past the threads on the cap over time. The fluid used in the brake system starts to deteriorate soon after it goes in with heat transfer and moisture because the system is vented. The darker the fluid the worse it is. If is was just topping of old fluid with the fluid on the shelf I would not worry about it. If I was flushing the system again I would always start with fresh fluid. 32 ounce bottle of fluid is likely ok for a system flush but you don't want to run out when doing the flush. Have extra and if it stays sealed then it's shelf life is nothing to worry about.