Sources of water in brake fluid

Sources of water in brake fluid

Author
Discussion

9xxNick

Original Poster:

767 posts

183 months

Wednesday 12th May
quotequote all
I need to understand if there's any way for water to enter into the brake fluid of a road car other than through absorption in the reservoir.

I don't believe there is, but would be interested to understand if there is any other mode by which the fluid can become contaminated by water, other than if already-contaminated brake fluid's been added to the reservoir.

stevieturbo

15,616 posts

216 months

Wednesday 12th May
quotequote all
If there are no obvious routes of entry....it should not really be possible.

9xxNick

Original Poster:

767 posts

183 months

Wednesday 12th May
quotequote all
That's what I thought. I'm faced with a situation where it should have been completely changed about 22 months ago, but is showing as >4% water, which makes me very suspicious that it wasn't changed when it was supposed to have been.

stevieturbo

15,616 posts

216 months

Wednesday 12th May
quotequote all
Supposed to have been changed because you paid someone to change it ?

Or supposed as in that's what the schedule states ? That almost nobody ever follows.

If any doubt, just have it changed now.

bulldong

3,417 posts

172 months

Wednesday 12th May
quotequote all
Has it got hot?

Chris32345

1,698 posts

31 months

Wednesday 12th May
quotequote all
stevieturbo said:
Supposed to have been changed because you paid someone to change it ?

Or supposed as in that's what the schedule states ? That almost nobody ever follows.

If any doubt, just have it changed now.
Most likely changed the fluid in the resivoir and nothing else

9xxNick

Original Poster:

767 posts

183 months

Wednesday 12th May
quotequote all
To answer the questions above:

Supposed to have been changed: Yes, because the garage charged for it and I've previously found them to be fairly good as garages go, which is why I haven't done a positive check on that aspect of their work before.

Has it got hot: I don't think so - it's my wife's car and she's not hard on it, and no one other than her and I have driven it.

Most likely changed the fluid in the reservoir and nothing else: Possibly, but even then I'd expect it to be below 4% water after less than two years.

Garage is supposed to be coming back to me this afternoon.

stevieturbo

15,616 posts

216 months

Wednesday 12th May
quotequote all
So I guess the next question...is how are you getting this >4% number ?

9xxNick

Original Poster:

767 posts

183 months

Wednesday 12th May
quotequote all
One of these Brake Fluid Tester

I don't have a lot of confidence that it's very accurate, but I've done a kind of baseline against fresh fluid, older fluid and a couple of other cars, and they all come up as expected with very low readings (<1%) so it seems likely the car really does have excess water in the fluid.


stevieturbo

15,616 posts

216 months

Wednesday 12th May
quotequote all
Interesting it looks like a clone of this Wurth tool.....Wurth make good stuff though.

https://www.mercateo.co.uk/p/8366-071553(20)200061...

Random ones from China...who knows.

Largely though if the fluid is a nice light colour, it's probably reasonably fresh. If darker, it may not be.

But not all fluids start the same colour, but they do tend to get darker with age.

9xxNick

Original Poster:

767 posts

183 months

Wednesday 12th May
quotequote all
I may have to do a quick check against new fluid which I've added a known amount of water to to see if the results look consistent with the percentage added. As said above though, the basic check against new fluid and cars with known good fluid checks out as <1%, with the suspect vehicle showing as >4%.

Caddyshack

3,668 posts

175 months

Wednesday 12th May
quotequote all
Google is your friend:

Brakes that use DOT brake fluid are more prone to water or moisture ingress. DOT brake fluid is hygroscopic by nature which means it absorbs water from the environment via seams and microscopic pores in your hydraulic lines.

9xxNick

Original Poster:

767 posts

183 months

Wednesday 12th May
quotequote all
Yup, I'm aware of that and it's the reason why it needs to be changed periodically. My problem is that I appear to have very water-contaminated brake fluid even though it was supposed to have been changed less than two years ago.

CoolHands

13,528 posts

164 months

Wednesday 12th May
quotequote all
You seem like an expert, so I’m surprised you don’t know how water got in there. Also how are you measuring it so accurately.

9xxNick

Original Poster:

767 posts

183 months

Wednesday 12th May
quotequote all
I believe I'm fairly familiar with how this works, but there's no harm in checking, since I'm not a mechanic by trade, just an interested amateur.

Measurement came from a device similar to the Brake Fluid Tester I linked earlier in the thread.

Caddyshack

3,668 posts

175 months

Wednesday 12th May
quotequote all
Some fluids are worse than others, I had dot 5 spf in a race car and the race mechanic said to change it very regularly as it was very hygroscopic.

I guess you cannot tell how long the mechanic had the fluid for before it went in your car (maybe they left the lid off) or if they did little more than drain the reservoir or just top up or did nothing and ripped you off.

GreenV8S

28,975 posts

253 months

Wednesday 12th May
quotequote all
Caddyshack said:
Brakes that use DOT brake fluid are more prone to water or moisture ingress.
That's good news, because the water that seeps into the brake system gets desolved into the brake fluid rather than collecting in pockets. Brake fluid contaminated with water still has a boiling point above that of water.

ncbbmw

368 posts

153 months

Wednesday 12th May
quotequote all
9xxNick said:
Yup, I'm aware of that and it's the reason why it needs to be changed periodically. My problem is that I appear to have very water-contaminated brake fluid even though it was supposed to have been changed less than two years ago.
Google searches suggest that 4% after 2 years is quite normal.


https://www.google.com/search?q=water+in+brake+flu...



9xxNick

Original Poster:

767 posts

183 months

Thursday 13th May
quotequote all
That's interesting. There are quite a lot of graphs that seem to be plotting the exact same data (DOT3 fluid with the same contamination levels over time) so it's possible that the source data is the same for all of them.

It's still odd though that every car manufacturer I've come across where I can recall the detail seems to think brake fluid changes every two years is fine, which would seem to contradict the data in the graph.

Evoluzione

6,630 posts

212 months

Thursday 13th May
quotequote all
If it bothers you use synthetic. When we order in BF now synthetic takes up 90% of the fluids available on the suppliers shelves, normal dot 4 is the remaining 10%. It's slowly being phased out.