Brake fluid will turn dark from being hot. That is normal and nothing to worry about. What is more important is it will absorb moisture from the air. That's why bottles of brake fluid, and the reservoir on the car, must remain closed and sealed when not in use. Moisture can also be absorbed through the porous rubber hoses too.
The problem with water in the fluid first of all is the corrosion problem with metal parts. In addition, brake fluid boils at well over 400 degrees. Water lowers the boiling point to 212 degrees. It's easy for the brakes to get that hot. The heat will transfer to the fluid and the water will boil and turn to vapor bubbles. Vapor compresses resulting in a mushy feeling brake pedal. This is one form of brake fade when they get hot.
Most people don't know or bother to change their brake fluid. It won't hurt to do it, but don't panic over it either. One thing that's real important is to not allow any petroleum product to mix with the brake fluid. Even wiping out an engine oil funnel and using it for brake fluid will contaminate the fluid. Rubber parts will swell and cause the brakes to drag. The only proper repair is to replace every part in the system with a rubber part, and to flush and dry all steel lines. This is a very expensive mistake. Even a little engine oil on your fingers can contaminate the fluid.
If you are familiar with the bleeder screws at the wheels, you can open them and just let the fluid drain slowly into a container, then refill the master cylinder with new fluid. Don't let it run dry or air will get into the system. You should not fill the fluid to the top though. Fill it to the same level it was at when you started. If it is a little low, that's because the front pads are partially worn and should be inspected. When new pads are installed, the front pistons will be forced back into their housings. That will force fluid back up into the reservoir. If it was filled previously, the extra fluid will spill out onto painted surfaces and the floor.
A different way to do half a job is to use a clean turkey baster to suck out as much fluid as possible from the reservoir, then pour new clean fluid in. At least a good percentge of the moisture will be removed.
If any parts of the hydraulic system need to be replaced, air will have to be bled out and a lot of old brake fluid will be removed that way. Old fluid is never put backk in. The mechanic will always refill the system with new fluid.
I never did this for customers so I can't tell you the cost for the service, but I would expect it to take around a half hour. A bottle of brake fluid should cost less than ten bucks.
Thursday, March 25th, 2010 AT 12:20 AM