Water in brake lines?

[yardape]

I procrastinated swapping in a new blower motor and so when I needed it, I had to have a garage replace it. While they had it they gave me a "complimentary inspection." We all know where that is going. They said I had water in my brake lines and that I needed to replace my coolant. Its been at least 5 years so I let them replace the coolant but was skeptical about water in the brake lines since its a sealed system. Having read a little it appears this is possible and that brake fluid should be purged and replaced periodically. I'd like some input from the gurus because it can cause the steel lines to rust from the inside out and fail just when you need them.
Thanks

 

[GrimmJeeper]

brake fluid is hygroscopic (it draws moisture out of the humidity in the air and retains it) which is why they say to never use a bottle of brake fluid that has already been opened and sitting. the main reason is water compresses, and oil does not. if the brake fluid absorbs too much moisture from the air it reduces its ability to apply pressure to the brakes. there's your science lesson for today

it could cause rust in the lines, yes. they usually rust from the outside in faster than inside out though in my experience. it could cause your brakes to not work as well, yes. Most mechanics (and the service intervals at the dealer) reccommend every 3 years or 25-30k miles or so having the whole system flushed so all of the fluid is brand new. Lots of people don't do this and are just fine but it's not that difficult to do yourself in the driveway with a helper to push the pedal down while you open the bleeder valve at each wheel.

if it's never been done that you know of, it would be a good idea to do it. when the fluid absorbs moisture and dirt it settles in the lowest point in the system, that would be the calipers and wheel cylinders. this can cause bits of rust to form and corrosion of the seals possibly leading to leaks or other problems some time down the road.

 

[Lurch]

Yes, it is possible. Brake fluid is hygroscopic and attracts water molecules. That's why they always say use fresh brake fluid from a sealed container when adding fluid to the system. I use the rule of thumb of flushing all of the old fluid from the system every two years.

I use a Motive power bleeder and it's makes the job a piece of cake.

Edit: Lol, Mike beat me to it. What he said.

 

[yardape]

Thank you. I learned something today.

 

[the_weirdo]

It's not that the water compresses, it's that the water affects the boiling point of the brake fluid. Pure DOT3 fluid boils at 401F, when it has water contamination of 3.7% it boils at 284F. If the brakes get too hot and there is water in the fluid it is easy to boil the fluid and lose all braking.

 

[8Mud]

It's not that the water compresses, it's that the water affects the boiling point of the brake fluid. Pure DOT3 fluid boils at 401F, when it has water contamination of 3.7% it boils at 284F. If the brakes get too hot and there is water in the fluid it is easy to boil the fluid and lose all braking.

Or have the steam build so much pressure it locks the calipers.

 

[winterbeater]

My old BMW shop manual recommended replacing brake fluid every 2 years. Seems like every 5 years would be a good idea.

 

[Hypoid]

What everyone else said, with emphasis on water collecting in the slave cylinders at the wheels. Once the ferrous parts start to rust, you in a heap-o-shite.

 

[Talyn]

What everyone else said, with emphasis on water collecting in the slave cylinders at the wheels. Once the ferrous parts start to rust, you in a heap-o-shite.

Water will not puddle at the wheel cylinders nor calipers. As said before the DOT3/DOT4 brake fluid will absorb the water.

 

[Hypoid]

That is interesting. How do the cylinders get rusted while the master does not?

 

[Talyn]

Heat, lack of fluid maintenance, & where they are located. I've also seen plenty of rusted master cylinders. Also, take note that the master cylinder is aluminum while the calipers are cast iron.