Here's something most fleet managers don't realize: glycol-based brake fluid is highly hygroscopic, meaning it actively absorbs moisture directly from the air. Even in a sealed braking system, brake fluid can absorb 2-3% water content per year through microscopic pores in rubber hoses and seals.
Why does this matter? The impact is dramatic. Fresh brake fluid typically has a dry boiling point above 230°C, but just 3% water contamination can drop this to around 140°C – a reduction of nearly 40%. In heavy braking scenarios, caliper temperatures regularly exceed 150°C, and contaminated fluid can vaporize, creating compressible gas bubbles in the lines. The result? Brake pedal goes to the floor with little to no stopping power.
This is why brake fluid specifications distinguish between dry equilibrium reflux boiling point (ERBP) and wet equilibrium reflux boiling point (WERBP). Modern formulations like DOT 4 are engineered to exceed both thresholds, maintaining performance even as inevitable moisture absorption occurs.
