Why is brake fluid important?
Brake fluid plays a crucial role in your braking system 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 braking or prolonged braking, 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 that your brake fluid can achieve 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.
Why does brake fluid deteriorate?
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. The boiling point can be significantly reduced by water contamination which will have a negative effect on your braking ability.
Whilst regular servicing of your vehicle will include checking the boiling point of your brake fluid, vehicle manufacturers recommend that you change your brake fluid at least every two years if not sooner (check your vehicle handbook for details). Changing brake fluid when recommended prevents brake failure and maintains the boiling point at a safe level.
The table below shows how the boiling point of DOT 4 ESP Brake Fluid can be severely reduced when it is ‘wet’ (i.e. contaminated with water) compared to when it is ‘dry’ (i.e. no water content like when the brake fluid is brand new)
|Dry boiling point (°C)||Wet boiling point (°C)|
|DOT 4 Standard||DOT 4 ESP Brake Fluid
||DOT 4 Standard
||DOT 4 ESP Brake Fluid