old brake fluid

[WmWatt]

The Haynes manual says when bleeding brake line always use new, unopened brake fluid. That's in chapter 9. In chapter 1 under checking brake fluid level it just says top it up, nothing about new, unopened. What do people do?

I bled the brakes 3 yrs ago and have 3/4 of the fluid left. I've been carrying it around in the car for "emergencies". The container just says to keep the lid on tight. I don't want to throw it out if it's still good. Besides being wasteful you're supposed to take it to a hazardous waste disposal site which is a bit of a pain.

[Larry Hampton]

As long as the lid is on and tight, there's less chance of it absorbing water, which is something brake fluid is bad about. Adding fluid is fine, as long as the lid stays closed while storing. Bleeding brakes is best done with new fluid.

I typically pour it in with my used motor oil that gets recycled.

[Christ]

Lol I have fluid that's about 10 years old... Been in a metal can the whole time, just used it to do the brakes on Herbie.

[WmWatt]

Looking at the container again I saw some numbers on the label which appear to be a date. I'm assuming expiry date. I'll be buying new fluid tomorrow.

Thanks for the tip on recycling. I'll pour the old fluid into my used oil container, an empty driveway sealer pail.

[Christ]

Too bad you're not closer to me, I'd collect your oil from you. I use it in Herbie.

[David88]

Good topic. I learned the hard way years ago with very expensive brake parts on classic cars. Don't store long term without bleeding the brakes. Brake fluid is hygroscopic. Open brake fluid, in two years, becomes 20% water. Not good for your brake system. Not for braking either as water will compress and could cause soft pedal feel. Bleed at least every two years.

[Zanzer]

^^ Yup! I change mine every 2 years or when I can look at the reservoir and it's dark, whichever comes first.

It never fails, when I tell people they should change their brake fluid at least every 2 years I get a look from them like I just showed a dog a card trick. :sad8:

[hotrodin4me]

i just changed my festiva over to Silicone Brake Fluid
never have to worry about them again.

[Zanzer]

^^ It's still a good idea to change it periodically. Especially if you put a lot of miles on the car. All brake systems regardless of the fluid used can get moisture in them. Silicon fluids don't absorb water like glycol based fluids and the water tends to puddle at the lowest point in the system. Many times this is around the steel piston in the caliper which will cause it to pit and can lead to leaks. Silicon can also compound this because it passes around seals and imperfections easier.

I'm not saying silicon is better or worse that glycol fluids. It's just something to think about

[nitrofarm]

Good topic. I learned the hard way years ago with very expensive brake parts on classic cars. Don't store long term without bleeding the brakes. Brake fluid is hygroscopic. Open brake fluid, in two years, becomes 20% water. Not good for your brake system. Not for braking either as water will compress and could cause soft pedal feel. Bleed at least every two years.

Water in brake fluid cause's corrosion to lines etc. And under extreme conditions the water can boil and cause rapid brake fade. But water is pretty much NON COMPRESSABLE. Just a little fyi.

[WmWatt]

I was interested to read on the Valvoline website that DOT 3 brake fluid is good in passenger cars because they are not negatively impacted when it begins to absorb water - whatever that means. I've found a lot of comments either way on the Internet but nothing from manufacturers or government safety regulators.

[Christ]

Water is a non compressible fluid, so water does not affect braking pressure application between the foot and the pads.

In extreme cases, the water, if not absorbed in the fluid, can phase change to steam, which creates pockets of dead space, making a spongy or, in serious cases, non existent brake pedal feel. Once cooled, it will return to normal.

It would require a SERIOUS amount of heavy braking to heat the fluid enough for this to occur, and heat fade would become a concern much sooner.

Pretty much the only thing to worry about with hygroscopic fluids is the deterioration that the presence of water can cause, including corrosion and damage to seals.

That said, I don't remember EVER doing a complete fluid exchange, and the only brake failures I've had were due to overworn pads, or line breakage due to exterior corrosion.

[WmWatt]

I bled the brakes this morning and hardly used any fluid at all. It came in a (450 ml, pint?) container with a long neck and the level when I was done was just at the bottom of the neck. So I topped the container up with the old fluid, screwed the lid on tight, and put it away for next time. There is no room in the new container for air so no absorption of H2O.

So little fluid was used because it was just charging new front calipers using the gravity method. Because I work alone I use the gravity method. I have used a stick of wood wedged between the seat and the brake pedal for the pressure method but prefer the gravity method. I was careful switching the line over from the old calipers so there was no air in the line and no bubbles came out. I took a photo of my home made bleeding apparatus and will put it in http://photobucket.com/Festiva-frontwheel when I get to the public library tomorrow.