What is this mystical liquid they call brake fluid? Some say brake fluid is what gives the fictional robotic assassin T-1000 from Terminator its super powers or if humans didn’t use brake fluid, the Large Hadron Collider would simply destroy the world in a black hole; and there would be no stopping it – pun intended!
Brake fluid is hydraulic in nature and what it is, it is an incompressible liquid. Brake systems take advantage of this capability to transfer pressure applied on one end of the system to the other end with minimal losses. In practice, this allows the foot pedal to operate the brakes – Thanks to the brake fluid. Brake fluid requires a clean and contaminant free environment to operate. However cars in the real world are exposed to all sorts of contaminants like heat, rain, dirt & moisture.
The brake fluid storage container aka reservoir, sits in a hot engine bay and that already gives the fluid a fair amount of heat to absorb. Remember the last time your bonnet was popped open and it felt like a sauna?
Heat can also come from hard braking from speed. Apart from the discs and pads heating up, the fluid supporting the pistons in the brake caliper will also heat up.
Moisture contamination is a larger player when it comes to maintaining the quality of brake fluid in the system. Moisture build up comes from many sources. Glycol-based brake fluid starts to absorb moisture from the moment it is put in the system. The fluid attracts moisture through microscopic pores in rubber hoses, past seals and exposure to the air. The problem is obviously worse in Singapore since humidity is high.
After only a year of service, the brake fluid in the average vehicle may contain as much as two percent water. After 18 months, the level of contamination can be as high as three percent. And after several years of service, it is not unusual to find brake fluid that contains as much as seven to eight percent water.
Our brake fluid tester reports the percentage of moisture present and displays either Green, Amber or Red depending on whether it has <0.1%, <1.5% or >3% moisture. Any moisture present is considered contamination. Water contamination increases the danger of brake failure because vapor pockets can form if the brake fluid gets too hot. Vapor displaces fluid and is compressible, so when the brakes are applied the pedal may go all the way to the floor without even applying the brakes hard.