Brake Fluid...

[AllenK]

Sure I could Google,but I like you guys.

Is it true that you should really throw away any unused brake fluid after you open a can? Call me crazy,but I swear I heard or read that somewhere. I've certainly never done that in the past!

Also,does brake fluid have a shelf life? I found a can of unopened brake fluid from 6 or 7 years ago. I'm about to have to do some brake work so I was just wondering about this subject.

[TheSilverBuick]

Re: Brake Fluid...

Brake fluid really likes to absorb water, even from the atmosphere. Water in brake fluid is no good. If sealed I don't see why it wouldn't be good. That being said I've never thrown any away after one use, but I do make sure I tighen the cap pretty good and don't let it sit with out a cap very long.

[min301]

Re: Brake Fluid...

Shelf life is forever, but once opened, brake fluid absorbs moisture.

[squirrel]

Re: Brake Fluid...

Old master cylinders had a vent in them, so it was a good thing to replace the fluid (bleed the brakes) pretty often. In the 60s they started using the rubber diaphram in the lid of the m/c, so modern systems don't absorb as much...but does it seal better than a capped plastic bottle? maybe, maybe not.

I live in Arizona, so I don't throw away partly opened bottles of brake fluid. I guess if you're anal about stuff like that, you might.

And a sealed bottle several years old wouldn't bother me either. I guess if you're anal about stuff like that, you might want to toss it.

[std]

Re: Brake Fluid...

The brake fluid we use is like $80 a liter, so no, we don't throw out a bottle after we open it. Just put the lid back on and it should be fine.

I would be a litle concerned about 7 year old fluid. Even if it's sealed, I think moisture can get in. For the price of a bottle, I wouldn't use it.

[fabricatordave]

Re: Brake Fluid...

i think brake fluid that sits that is still in a can tends to go yellow toward orange as it absorbs moisture. a new one the fluid is almost water clear. so the darker it is the more moister it has absorbed

[Woodward_Dreams]

Re: Brake Fluid...

Ok according to my teacher (at a local tech school), brake fluid can technically take in water through the plastic bottle, but technically the shelf life is forever. But once opened, i think it's 60 days until bad. once it obsorbs more than 2-4 percent of the brake fluid's mass, stopping times are significantly reduced. thats what i was told anyway.

[bnjny]

Re: Brake Fluid...

Brake fluid is hydroscopic. It does absorb water. My rule of thumb is if less then half full 9the bottle) and more than six months old toss it. If more then half full, test it (they do make little strips that are not too bad for the $$).

[HoosierGTA]

Re: Brake Fluid...

If its the guy at work that give you problems all the time but thought he'd do you a favor because he thinks you like to work on cars,it's fine.

[Caveman]

Re: Brake Fluid...

You're dead on about it absorbing water...

My sister had a 4Runner with 200k on it, and her clutch was borderline... wouldn't release all the way. Bled it, topped it off, and good as new... right up until we had some rainy weather for a week or two. After the rain, it got to the point where the truck would be moving in gear, clutch fully depressed. No leaks, re-bled, topped off again, no prob, fixed. Turned out the rubber cap was old/loose, letting humid air in... which the fluid promptly absorbed.

[CaminoKid]

Re: Brake Fluid...

Please educate a dumb man. Are we saying that brake fluid absorbs water.or are we saying that it attracts water to the void not occupied by brake fluid. Last i checked oil and water don't mix.but maybe brake fluid is not oil.

[CTX-SLPR]

Re: Brake Fluid...

Brake fluid is not an oil, not exactly sure what it is but it is a polar compound that will absorb water. The water is solvent in the system and will fill in the spaces between the brake fluid molecules and becomes part of the fluid just as you can add sugar to water but not increase the volume until you reach saturation. We used lots of penetrant oils that were hydroscopic and we had to keep them tightly sealed in glass bottles and kept inside of a desicated container to prevent them from going bad. We also tested them with a refractometer to test the disolved water content.

[CaminoKid]

Re: Brake Fluid...

Thank You

[Blazerteam]

Re: Brake Fluid...

I have learned a bit about brake fluid the last years.Road racing a 76 Chevelle at track days with the original brakes requires new brake fluid every year at least.If it has been warm or cooked,it must be changed.

I have tried to not change it between track days,and it boils faster if it has been boiled before.Simple as that.

The other benefit of changing brake fluid often,is that when the car goes thru the tech at track,and they check the quality of the brake fluid.I get the license to drive and lazy owners of modern cars get the thumbs down ;D.

This summer a 4 year old mercedes slk got the thums down right in front of me,and the face of the owner was priceless when a scruffy chevelle sailed thru ;)

[malc]

Re: Brake Fluid...

I get this muck in my reservoir, hard to define what it is.
I use a sryinge to suck out the fluid and replace with new,
bleed the brakes and add more if needed.
The master cylinder was overhauled several years ago, down at
the brakes end it comes out clean.