Brake fluid has crazy high water %. Ideas?

[Molez93]

Two testers indicate 4%+ water in my reservoir. I bled the system completely last Oct, and it showed really high water at that time too. The system otherwise functions fine & no leaks as far as I know, though I don't really push the brakes hard on the X5M.

Any thoughts on what my core issue might be? Never had anything like this in 30 years of doing some of my own maintenance.

[Molez93]

Not sure if this is even more unusual than I thought or if I asked the question in an unclear way...

Is there a way to solve this water problem without just throwing parts at it?
Given how much water has been in there and for how long, I won't be surprised when I need to replace the whole system (master cylinder, booster, calipers, and lines etc.) at some point.

[Molez93]

Based on some feedback on another, non-BMW forum I've ordered a new reservoir cap. Mine is likely original to the vehicle, and $45 is a reasonably cheap part to throw at it on the chance it solves my problem.
However, I'd still welcome any X5 specific suggestions or thoughts on how the !@#k the water is getting in there so quickly.
TIA!

[Molez93]

OK- last one unless people reply...
The tone of the replies on that other forum suggest they don't think this is really an issue.
"Just bleed the system more often" is the gist of much of that feedback.

Am I over reacting to the water %?

[Colodano]

Admittedly I have never tested brake fluid for water in any of my cars, but the cap or a leak somewhere else are the only options that I can come up with.
The one car that I did a bunch of brake modifications on, I would do a full fluid replacement every couple of years, and I switched between the Ate blue fluid, and Motul, so it was very obvious when the system was flushed with the old fluid and had all new fluid.

[Molez93]

After a ton of discussion on another forum about this situation generally (not specific to an X5), I'm convinced my problem may start and end with the inexpensive conductivity testers I'm using. The $10 Amazon-type devices are likely less reliable than I'd thought- possibly useless.
I just bought a real boiling point tester for ~15x the price of what I have already. I might be throwing money at a non-problem (fluid looks good, performs fine, known to be ~6 months old), but I want to be able to check fluid in my garage regardless.

[Molez93]

The real boiling point testing device showed essentially the same as the cheap probes:
Actual boiling point of 182C
New fluid bp of 250C (Pentosin LV)

[yco]

i dont want to sound "smart" that much but..

1. did you fill up the brake fluid from a bucket or something? cause brake fluids are a bit weird.. they suck the moisture so easily.. or so if you somehow used a brake fluid bottle was already open for a while like even 2-3 hours or put it in a different bucket etc. it can suck moisture and under pressure it can cause bubbles even easier..

2. are you sure that you have 4 brake calipers are not continuously rubbing the discs too much can cause extra heat? are you sure all 4 100% ok?

3. most importantly do you have spongy brake pedal? push the brakes a bit and if you dont have spongy brakes then it can mean there is not a problem.. not talking about the brake fade of course here..

4. are you 100% sure there is not much corrosion on the brake system?

5. are you 100% sure that brake cylinder is ok?

6. maybe the most important.. is this an OEM brake fluid you used?

[Molez93]

Originally Posted by yco

i dont want to sound "smart" that much but..

No worries. I believe I know and execute sound maintenance practices, but I asked because I'd like to be better at this...

> 1. did you fill up the brake fluid from a bucket or something?
I filled a Motive pressure bleeder with freshly opened Pentosin DOT 4 fluid from three different 1l metal cans. That pressure bleeder was dry with no obvious contaminants having cleaned it out previously with denatured alcohol months before.

> 2. are you sure that you have 4 brake calipers are not continuously rubbing
> the discs too much can cause extra heat? are you sure all 4 100% ok?
Could be, though there are no signs of that based on brake feel or visual inspection of the parts.

> 3. most importantly do you have spongy brake pedal? push the brakes a bit
> and if you dont have spongy brakes then it can mean there is not [...]
Not spongy at all. Firm with ignition 'off,' and 'on,' and after driving around. I have not *tried* to overheat the things with repeated, aggressive stops...but they would probably get spongy from that given the BP right now.

> 4. are you 100% sure there is not much corrosion on the brake system?
Actually, I'm pretty sure there is some corrosion. When I bled the system last fall, both rear bleeder screws were crusty. One barely turned enough to bleed normally. The nipple/hole on the other was clogged (I believe even with the rubber cap in place) to the point where I needed to bleed that caliper by backing the screw *just* far enough out to release fluid at the screw's base and not from the nipple.

> 5. are you 100% sure that brake cylinder is ok?
Nope. Definitely not, assuming we're referencing the master cylinder. No signs of leaks though. Nothing I can see at the booster or fluid reservoir either.

> 6. maybe the most important.. is this an OEM brake fluid you used?
OE spec- I think. I forget the site (FC Euro, Pelican, etc), but Pentosin was what seemed to be suggested. The primary difference was that my retailer (OEMPartHaus in Texas) shipped regular Pentosin DOT 4 instead of the LV (low viscosity) I'd ordered. I didn't realize the error until I was halfway done with the work. [It also happens that I'll never do business with OEMPartHaus again as they were the *worst* to deal with of any vendor I've used in the 30 years I've been buying car parts online... but I digress]

So my immediate next step is to bleed the system again with changes:
- replace the rear calipers with good condition used ones which don't have the signs of corrosion like my existing set of rears
- replace the fluid reservoir cap with a new, OE part
- use Pentosin DOT 4 LV fluid