dapopa9

I have always heard that an open container of brake fluid would be quickly contaminated if not used up quickly and thus shouldn't be saved for later use in the car. What is an acceptable period of time to still use the fluid after the bottle has been open?

I was just thinking that most cars have the same brake fluid in them for 1 or more years. Wouldn't that be the same as storing it in the bottle for a year?

Werks

I use the same brake fluid for my clutch also. So when I open a bottle I use it to bleed my brake and any left is used to bleed the clutch at the same time. I never save an already opened bottle of brake fluid, use what you need and then dispose of the ballance. If you have way too much look into buying smaller bottles.

ZedO6

For track use...I will only use fresh from a sealed container. Any left over goes to the track for that weekend and after that is relegated to street car use. For track use you want brake fluid as close to the dry boiling point as possible. We know brake fluid absorbs moisture with time and use, so I consider anything not fresh out of a sealed can at best, degraded to the wet boiling point. When bleeding, I try to get to the point where I use up all the open fluid.

For the street, completely different story. With a typical 2-3 year bleeding cycle, tightly capped brake fluid is fine for top up but should not be used when you are doing your annual or every 2 year brake fluid bleed IMHO.

froggy47

That's a good system.

dapopa9

So I guess more to the point here....storing it in the original opened bottle is really no different than it sitting in the car in the brake/clutch system?

CHJ In Virginia

I am going to take a contrarian position on this debate. If the cap is screwed on tight, fluid will stay good for quite some time. There is not enough water vapor in a container to make a hill of beans in difference in fluid performance. I open and use a can of ATE super blue over about a 3 - 4 month time frame. Bleed every event till caliper flows clean and let it go at that. Never had a problem, just make sure that the cap is on securely. If you leave the cap off on the can for several days - all bets are off.

ZedO6

Brake fluid is hygroscopic, which means it's trying to absorb moisture. In actual use, the fluid goes through a temperature cycle that produces condensation in the vehicle's fluid reservoir, this condensate is then absorbed by the brake fluid. This is much different than storing brake fluid in a partially full sealed container.

The only issue with a open container of brake fluid is the empty part of the container, that is the "atmosphere" portion of the original container. The brake fluid will absorb moisture from the "gas" part of the sealed container. If you could transfer the brake fluid to a smaller container that had no "air void", the amount of moisture absorbed by the remaining fluid would be very low. Brake fluid stored this way would be closer to the original dry boiling point.