I'm not doubting that water in the brake fluid is bad news, I'm just trying to point out that a system that isn't opened up generally doesn't get water in it in the first place. My brake fluid was due for a flush when Bush Sr took office, yet I didn't have to replace it until my master cylinder conked out just six months ago.
A glowing hot rotor is going to seriously accelerate fluid boiling, though. Especially with the metal calipers used on my front brakes that act as big-ass heat sinks. Honestly I'm surprised the fluid didn't boil. By all accounts it should have, even without water contamination, as it simply wasn't specified to deal with the heat in the right front brake AND it was several years and over a hundred thousand miles past due for a change. I also lucked out on the rotor, it didn't warp, although I did crack the brake pad linings slightly.
Yes. It. Does. Every brake system gets water in it, you can search it on google if you dont believe me. Every year a certain percentage of water gets into the brake system. i'm talking bout 5% in a couple of years, but it makes the difference. And believe me, the fluid gets much hotter when you, by example, drive up and down mountains, where you have to take big use of braking, and the fluid gets under big pressure. The pressure makes the fluid very hot, and you will really feel the difference after a while in how much worse the brakes work when you went down a few hills. So if there's water in the system, the point at where the brakes start to work less good, will be much sooner. YOu know what, i'll google it just to have some real numbers about it, because i can't say for sure myself:
Most automotive professionals agree that glycol-based brake fluid, (DOT 3, DOT 4, DOT 5.1) should be flushed, or changed, every 1–2 years.[2] Many manufacturers also require periodic fluid changes to ensure reliability and safety. Once installed, moisture diffuses into the fluid through brake hoses and rubber seals and, eventually, the fluid will have to be replaced when the water content becomes too high.
Many experts have long recommend changing the brake fluid every year or two for preventative maintenance. Their rationale is based on the fact that glycol-based brake fluid starts to absorb moisture from the moment it is put in the system. The fluid attracts moisture through microscopic pores in rubber hoses, past seals and exposure to the air. The problem is obviously worse in wet climates where humidity is high.
After only a year of service, the brake fluid in the average vehicle may contain as much as two percent water. After 18 months, the level of contamination can be as high as three percent. And after several years of service, it is not unusual to find brake fluid that contains as much as seven to eight percent water.
An NHTSA survey found that the brake fluid in 20% of 1,720 vehicles sampled contained 5% or more water!
As the concentration of moisture increases, it causes a sharp drop in the fluid's boiling temperature. Brand new DOT 3 brake fluid must have a dry (no moisture) boiling point of at least 401 degrees F, and a wet (moisture-saturated) boiling point of no less than 284 degrees. Most new DOT 3 fluids exceed these requirements and have a dry boiling point that ranges from 460 degrees up to over 500 degrees.
Only one percent water in the fluid can lower the boiling point of a typical DOT 3 fluid to 369 degrees. Two percent water can push the boiling point down to around 320 degrees, and three percent will take it all the way down to 293 degrees, which is getting dangerously close to the minimum DOT and OEM requirements.
DOT 4 fluid, which has a higher minimum boiling temperature requirement (446 degrees F dry and 311 degrees wet) soaks up moisture at a slower rate but suffers an even sharper drop in boiling temperature as moisture accumulates. Three percent water will lower the boiling point as much as 50%!
Considering the fact that today's front-wheel drive brake systems with semi-metallic linings run significantly hotter than their rear-wheel drive counterparts, high brake temperatures require fluid that can take the heat. But as we said earlier, the brake fluid in many of today's vehicles cannot because it is old and full of moisture.
Water contamination increases the danger of brake failure because vapor pockets can form if the fluid gets too hot. Vapor displaces fluid and is compressible, so when the brakes are applied the pedal may go all the way to the floor without applying the brakes!
Anything else?