Sources of water in brake fluid
Discussion
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.
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.
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.
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.
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.
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.
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.
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.
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%.
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.
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.
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.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...
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.
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.
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