Regarding brake fluid exchange to remove "moisture" and prevent system degradation- I have wondered if the "moisture" in brake fluid that vaporizes when the brakes get hot, can return the fluid to original moisture free condition. Just hit the brakes hard several times (on an empty road, of coarse) and get a brake flush "on the go"?
Brake Fluid Exchange
- Thread starter willbur
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edyvw
$50 site donor 2025
What did I just read?
No.
Water has a much lower boiling point than brake fluid. Water vapor is absorbed out of the environment by brake fluid (brake fluid is hygroscopic...look it up if you don't know what that means), mostly from the vented reservoir cap opening(s). Once absorbed, when brake fluid is heated sufficiently it "boils" which results in "air" in the lines..in reality, this isn't air but it is "outgassing" of water vapor. Outgassed water vapor is compressible, which is NOT what you want in a hydraulic system...so the brake pedal will feel "spongy" and there is a decreased ability to apply pressure on the brake pistons which push the pads against the rotors....and the hotter the fluid, the more the outgassed bubbles increase in size, making the hydraulic system less and less able to function correctly. So heating up the fluid is not the answer to water vapor...heating exacerbates the problem. Suffice it to say that you do not want compressible gas in a brake line, whether it is water vapor or actual air (which can happen if the fluid level gets too low and frank air is sucked into the system).
I sense a real scientist here... LOL I dunno- makes sense to me. Water vaporizing from the fluid causes brake fade. Logically, then, any vaporized water leaving the system is what you are doing if you remove it by draining it out
Ha. Sounds like you maybe outgassing your self with this gibberish
if you put on your glasses, you will see a tiny vent hole on the top of the fluid reservoir
This is just a thought experiment. I flush when my voltage reading in the fluid tell me to. Or 30K
Where will it vaporize too?
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I believe getting the fluid hot enough throughout the system isn't possible.
If it were hot enough near the wheels, would it be hot enough in the reservoir?
The cooler fluid would probably absorb whatever moisture was expelled from the hot fluid.
edyvw
$50 site donor 2025
Please just change fluid.
Glad you change it at a decent interval, but I do not believe you will get the results you are looking for by braking hard instead you are just causing unnecessary brake pad and rotor wear.
Brake fluid is hygroscopic so it will absorb moisture no matter what which, but it is also a closed system which means there is nowhere for that moisture to evaporate to even if you got it hot enough it would just turn to water vapor and condensate and cool and turn back into liquid, this is why it is important to change brake fluid out every few years or around that 30-40,000 mile range some manufacturers even recommend it being done earlier, and of course there is other important reasons.
So you seem to be saying it will rise. In my thinking, the first part of the hydraulic system to get hot will be the calipers. So wouldn't it rise to the top of the calipers, ie by the bleeder screw and sit?
I'll take that as an attempt at humor.
it isGot it. But let me explain. Ford engineers visited auto recycling yards and took many samples of brake fluid. Probably the best place to collect brake fluid for moisture testing. Contrary to expectations, they found very little. So.. I'm just sitting here and the thought pops in my head that perhaps no moisture was found bc it boils off as the brakes are used. Hence my comment re brake flush on the go. Just a thought experiment
What has been found is copper leachate from the metal lines that corrode the system (this probably drops off after the first fluid flush) So, by changing out the brake fluid bc of "moisture" one is actually protecting the system from copper corrosion. And that's what i do.
Good point- You maybe right. The vapor rises up bc its a gas to the reservoir and "burps" out with brake application. Note that its a gas bc a spongy pedal is felt, meaning it travelled up to the master cylinder/reservoir
Please share more information on this experiment. A link or source would be enlightening.
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