Brake fluid plays a crucial role as it transfers the force created when a driver presses the brake pedal directly onto the wheel hub. Heat generated under braking, especially under heavier breaking or prolonged breaking, may affect the brake fluid which can only work if it is liquid and not so hot that it has become vapour. Therefore the boiling point your brake fluid achieves is critical to efficient braking as temperatures above the boiling point form vapour bubbles in the system, potentially resulting in brake failure.
In addition, the brake fluid serves as a lubricant of all movable parts and prevents corrosion. It has to be compatible with rubber seals and hoses thus allowing braking systems to achieve long service and optimal performance.
A brake fluid has hygroscopic properties - meaning that it absorbs moisture during its life in your car through the pipes, hoses and joints that it lubricates. As the water content in the brake fluid increases, the temperature the liquid boils at decreases from when the brake fluid is ‘dry’ (ie no water content when new) to when it is ‘wet’ (contaminated with water).
The boiling point can be significantly reduced by water contamination below 5%. See below the difference in boiling temperatures for DOT 4 ESP Brake Fluid and how it exceeds the international standards for performance (known as the DOT standard).
|Dry boiling point (°C)||Wet boiling point (°C)|
|DOT 4 Standard||DOT 4 ESP Brake Fluid||DOT 4 Standard||DOT 4 ESP Brake Fluid|
Whilst regular servicing will check the boiling point of your brake fluid, vehicle manufacturers recommend that you change your brake fluid a maximum of every 2 years if not advised to before. Changing brake fluid when recommended prevents brake failure and maintains the boiling point at a safe level.