Brake Fluid: Testing and Inspection

REPLACEMENT GUIDELINES
Replacing brake fluid is recommended every 48000 km (30 000 miles), or every other year. In cars where the brakes are used and often (e.g. in hilly areas or in tropical climates where humidity levels are high), fluid should be refaced each year.

BACKGROUND
The reason that brake fluid should be changed is that brake fluid is hygroscopic: that is, it absorbs water molecules from the air. Water is partly absorbed through the brake hoses and brake fluid reservoir, which are made of rubber and plastic respectively, and are to some extent permeable to water molecules. Increasing the water content of brake fluid means that the brake fluid's boiling point falls dramatically and that corrosion forms on the braking system components. The result is that the braking system is damaged and its functioning seriously impaired.