Is modern brake fluid less hygroscopic?
Discussion
Today I changed/flushed the brake fluid on my Jaguar XE. It's been in there for at least 7 years and possibly longer (yeah yeah I know).
I regularly change the brake fluid on my other cars (one is for racing and so it gets bled every month or so) and so I was expecting the fluid coming out of the calipers to look a bit manky (on my race car, the fluid from the rear calipers always looks nasty).
To my surprise, the fluid looked absolutely fine and incredibly clean, and so I tested it for moisture content. The tester showed no moisture (or more accurately less than 1%).
This car gets used in all weathers, the brakes occasionally get worked etc etc. And so... is modern brake fluid simply less hygroscopic or is this "change fluid every 2 years" malarky just a nonsense for a normal car??
I regularly change the brake fluid on my other cars (one is for racing and so it gets bled every month or so) and so I was expecting the fluid coming out of the calipers to look a bit manky (on my race car, the fluid from the rear calipers always looks nasty).
To my surprise, the fluid looked absolutely fine and incredibly clean, and so I tested it for moisture content. The tester showed no moisture (or more accurately less than 1%).
This car gets used in all weathers, the brakes occasionally get worked etc etc. And so... is modern brake fluid simply less hygroscopic or is this "change fluid every 2 years" malarky just a nonsense for a normal car??
Ooh good question! I would have thought technology has improved over the years in the same way as engine oils, but while we now have long life condition based oil changes, OEM's are still saying 2 years for a brake fluid change. You'd think OEM's would be the first to make servicing costs cheaper for that fluid as well, so maybe there's other factors in play.
I think a lot of that depends on the design and condition of the reservoir. Old systems used to use a crude baffle which didn't seal particularly well. More modern ones seem to use bellows which seal much better. If you eliminate exposure to fresh air, the only path in for moisture is via seals and hoses, which should have very low porosity if they're in good condition.
LennyM1984 said:
Today I changed/flushed the brake fluid on my Jaguar XE. It's been in there for at least 7 years and possibly longer (yeah yeah I know).
I regularly change the brake fluid on my other cars (one is for racing and so it gets bled every month or so) and so I was expecting the fluid coming out of the calipers to look a bit manky (on my race car, the fluid from the rear calipers always looks nasty).
To my surprise, the fluid looked absolutely fine and incredibly clean, and so I tested it for moisture content. The tester showed no moisture (or more accurately less than 1%).
This car gets used in all weathers, the brakes occasionally get worked etc etc. And so... is modern brake fluid simply less hygroscopic or is this "change fluid every 2 years" malarky just a nonsense for a normal car??
I'd say it's a rarity that cars have their brake fluid changed every 2 years.I regularly change the brake fluid on my other cars (one is for racing and so it gets bled every month or so) and so I was expecting the fluid coming out of the calipers to look a bit manky (on my race car, the fluid from the rear calipers always looks nasty).
To my surprise, the fluid looked absolutely fine and incredibly clean, and so I tested it for moisture content. The tester showed no moisture (or more accurately less than 1%).
This car gets used in all weathers, the brakes occasionally get worked etc etc. And so... is modern brake fluid simply less hygroscopic or is this "change fluid every 2 years" malarky just a nonsense for a normal car??
First time most will see new fluid, is if it needs a caliper or some other work that necessitates it. And even then, it'd be just for that item, not a complete fluid change.
I am sure brake fluid has improved over the years. But notice how brake fluid changes every two years became a thing about the same time as servicing changed to yearly or longer… call me cynical but…
There was a poster on here called Max Torque, sadly gone now, and he said in a relatively low humidity country like ours there just isn’t enough moisture in the air to effect the brake fluid.
Which bakes up the years, well over ten now, of testing brake fluid and I have never seen a reading over 1%.
There was a poster on here called Max Torque, sadly gone now, and he said in a relatively low humidity country like ours there just isn’t enough moisture in the air to effect the brake fluid.
Which bakes up the years, well over ten now, of testing brake fluid and I have never seen a reading over 1%.
Edited by Megaflow on Saturday 27th April 09:17
Perhaps it is more about trying to encourage people to have the brakes bled every so often? I suppose that "flushing the fluid so that it doesn't boil and kill you" sounds more persuasive than, "let a little air out," despite largely being the same thing.
My brakes obviously feel much better now but that's simply because I was able to bleed some trapped air out
The fluid in my race cars has also never shown any significant moisture absorption but it does tend to get manky.
My brakes obviously feel much better now but that's simply because I was able to bleed some trapped air out
The fluid in my race cars has also never shown any significant moisture absorption but it does tend to get manky.
Depending on the car, I find the fluid starts to degrade anything between one and three years. My Elise typically gets a change annually, as even after a year the fluid has 2% moisture content.
I do the pair of “modern classics” every two years - on testing they’re typically sub 1% after two years, but for the sake of a litre of fluid, and twenty minutes of my time at service…the brakes do feel a little better after doing so. It may be placebo, but it’s worth it for my peace of mind.
The 23 year old shed I’ve just acquired had properly brown fluid that lit up every light on the tester! That got changed pronto, along with a major service and replacement of the cambelt that had been on there since 2006!
I do the pair of “modern classics” every two years - on testing they’re typically sub 1% after two years, but for the sake of a litre of fluid, and twenty minutes of my time at service…the brakes do feel a little better after doing so. It may be placebo, but it’s worth it for my peace of mind.
The 23 year old shed I’ve just acquired had properly brown fluid that lit up every light on the tester! That got changed pronto, along with a major service and replacement of the cambelt that had been on there since 2006!
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