Used brake fluid

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Some say open (broken seal) bottle of brake fluid in the garage goes bad after a while and absorbs moisture ...
How is it that moisture is not an issue in old cars. Most never change or flush brake fluid.

brake fluid doesn't cost much but curious why it's ok to sit the car and not in the bottle. Maybe the car reservoir cap has a better seal but people open the reservoir cap once in a while and it can't have a perfect seal.
 
It does go bad. If one was to check the moisture content of brake fluid in old cars that had not been changed in years; it would be found to have an unacceptable high water content, lower boiling point and probably unacceptable copper levels.
 
It's hygroscopic and absorbs moisture sitting in the opened bottle or master cylinder. The idea is that if you're adding it to the brake system, it might as well be as fresh as possible.
 
I have used brake fluid from a previously opened bottle with no issues whatsoever.No change in color or transparensy,no brake performance issues or wierd petal feel.I think the manufacturer wants to be sure mainly in the case that the brake fluid might get contaminated from dirt (windy weather,dirty workplace) or someone forgets to close the lid , leaving it open for weeks etc. and then use it again.
If no dirt gets in the fluid and the lid is opened only for the required time and closed properly,I believe that the fluid is ok to use and much healthier and pure than any used fluid that comes out of a brake system.
 
I'm not saying anyone is actually going to notice water in their brake fluid as a performance issue or with things rusting out, but brake fluid is hygroscopic and absorbs water. It will lower the boiling point of brake fluid eventually and cause corrosion and acid. Does it really matter? Probably depends on how bad it gets and how bad that high speed panic stop on the highway means to you, and let's face it, the brake fluid will probably be the least of your worries...the pads, and rotors (if worn out) will be a much bigger issue.

And you can't "see" the water in the brake fluid - which I thought you could - it supposedly disperses evenly throughout the fluid. There are test strips that will tell you if it's saturated. They say it dispersed evenly to prevent the water from building up in one area and causing that one area to boil - which I don't think was intentional when they developed brake fluid - I think manufacturers have a way of taking credit for things, and making it seem like that's what they intended all along. If they intended to do that...why not just make it so it doesn't absorb water at all?
 
Originally Posted by Railrust
I'm not saying anyone is actually going to notice water in their brake fluid as a performance issue or with things rusting out, but brake fluid is hygroscopic and absorbs water. It will lower the boiling point of brake fluid eventually and cause corrosion and acid. Does it really matter? Probably depends on how bad it gets and how bad that high speed panic stop on the highway means to you, and let's face it, the brake fluid will probably be the least of your worries...the pads, and rotors (if worn out) will be a much bigger issue.

And you can't "see" the water in the brake fluid - which I thought you could - it supposedly disperses evenly throughout the fluid. There are test strips that will tell you if it's saturated. They say it dispersed evenly to prevent the water from building up in one area and causing that one area to boil - which I don't think was intentional when they developed brake fluid - I think manufacturers have a way of taking credit for things, and making it seem like that's what they intended all along. If they intended to do that...why not just make it so it doesn't absorb water at all?



The fact that it attracts water like crazy is exactly why the water is evenly dispersed.
 
Originally Posted by Panos
I have used brake fluid from a previously opened bottle with no issues whatsoever.No change in color or transparensy,no brake performance issues or wierd petal feel.I think the manufacturer wants to be sure mainly in the case that the brake fluid might get contaminated from dirt (windy weather,dirty workplace) or someone forgets to close the lid , leaving it open for weeks etc. and then use it again.
If no dirt gets in the fluid and the lid is opened only for the required time and closed properly,I believe that the fluid is ok to use and much healthier and pure than any used fluid that comes out of a brake system.

I have too, as have millions of other people. Is it the best method? No, but I flush my brake fluid every two years, and if for some odd reason I need to add an ounce or two the fluid in the container left over is better than what is in the brake system. And odds are very high that I have a leak and have to address it. At that point I am replacing something that is leaking and will add fresh new fluid to complete the job.
 
Opened cans get combined and I try to seal the cap the best I can and they are thrown into the Jeep for emergencies on the trail. But I always buy the little cans for myself. That way I'm not wasting the big 1qt bottles of it .

I used to think that brake fluid flushes were a scam. Until I was in heavy traffic down south on a very hot day and had the brake pedal go to the floor because the fluid boiled.

Thankfully whatever highway we were on in GA did not have a barrier! Had to run down the median and use the parking brake to stop.

Since then, I am a frequent flusher. Luckily, on my older vehicles I change the fluid frequently as I'm always changing calipers or wheel cylinders.
 
It's all good until you have your beloved family in the car, towing the camper down a mountain, and the brakes get hot. Once the fluid boils, the pedal goes to the floor and you have to white-knuckle it until you see a run-away truck ramp...
 
If we could see the inside of the brake lines, I think we would bleed out the old brake fluid more frequently. Especially in older vehicles.
 
Brake fluid has corrosion inhibitors in there also. While it is true that it will begin to absorb moisture, there is no metal. So the corrosion inhibitors should not be getting depleted.

I used them if I need to top up, but not for the flushing process.

Rod
 
When I was a kid I had a '53 Pontiac that of course had practically nothing in the way of passenger safety, including a single brake-line system.

The car had been hit in the left rear fender and had been fixed just before I bought it.

One evening as I approached a red light the brake pedal sank to the floor. I coasted across eight lanes of traffic before the thing would stop with the "emergency" brake, but with, amazingly, no two objects occupying the same space. The body shop had fixed the fender, but unnoticed was the brake line that had been pinched and had split.

Being an ignorant kid I knew nothing about checking brake fluid, but even if I had, being immortal, I probably wouldn't have checked it anyway, because the master brake cylinder was under the floor, whereas the radio wasn't so it was fixed first.

The mechanic at the Esso where I had the brake line fixed explained about brake fluid and its habit of attracting water and boiling, causing bubbles and sailing across eight lanes of traffic, or worse.

Any used car I bought after that always had its brakes bled, just as it always had an oil change. I get new fluid every three years. I won't even unscrew the lid of the now-visible master-cylinder. (I would if the thing was really low.) My car's due now. The problem, though, is finding a shop that would let me watch to see if the job is thorough and making sure the mechanic isn't using fluid from a previously opened bottle.

I'd do it myself, but thereby lies ruin and death. I'm a klutz of the first water. But I suppose that helps the economy.
 
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