You should flush and replace the brake fluid in your brake system every two years. You can change your own brake fluid, but service facilities now do this with brake flushing machines. If you find have a brake fluid leak or you have to bleed your brakes, you’ll have to restore the brake fluid in your master cylinder to its proper level. Here are some things that you should know about buying and using brake fluid:
Always use top-quality brake fluid from a well-known manufacturer: Many vehicles call for either D.O.T. 3 or D.O.T. 4 fluid. D.O.T. 5 is now available, too; it’s a great improvement because it doesn’t eat paint or absorb moisture. The downside is that because D.O.T. 5 doesn’t absorb it, water that gets into your brake system can form little pools that can corrode your brakes.
Exposure to air swiftly contaminates brake fluid: The oxygen in the air oxidizes it and lowers its boiling point. Brake fluid also has an affinity for moisture, and the water vapor in the air can combine with the brake fluid, lowering its boiling point and, in cold weather, forming ice crystals that make braking difficult. Adding fluid contaminated with water vapor to your brake system can rust the system and create acids that etch your wheel cylinders and master cylinder and foul your brakes, causing them to work poorly — or not at all. It can also destroy vital parts of ABS and other expensive braking systems.
If you’re just going to add brake fluid to your system, buy a small can of the correct type, add the fluid to your master cylinder, and either throw the rest away or use it only in emergencies. The stuff is pretty cheap, and your vehicle shouldn’t need more fluid after you fix a leak. If you keep a can with only a little fluid left in it, the air that fills up the rest of the space in the can contaminates the fluid no matter how quickly you recap it.
Keep brake fluid away from painted surfaces: If this stuff seems scary, remember that the same statements can be made about turpentine and nail polish remover.
Remove the old, dirty fluid from the master cylinder reservoir.
Use a cheap turkey baster for this.
Use a lint-free cloth to wipe out the reservoir.
Do this only if you can get in there.
Pour new brake fluid into the reservoir just until it reaches the “Full” line, replace the cap on the reservoir.
As you bleed the brakes (which you can find out how to do elsewhere on this site), the new fluid pushes the old fluid out of the system. Continue to bleed the brakes until you see clean, clear fluid exiting the bleeder screw.