Why Mercedes-Benz Brake Fluid Service Matters

hygroscopic

[hahy-gruh–skop-ik]

adjective

1.absorbing or attracting moisture from the air.

From <http://www.dictionary.com/browse/hygroscopic>

One of the most overlooked service items in any car is the brake fluid. Brake fluid is typically a Glycol Ether based fluid (DOT 3, DOT 4) which gives it a low freezing point and more importantly a high boiling point to avoid vaporizing in the system. In order for your brakes to work properly the brake fluid must remain a non-compressible liquid (Google search Pascal’s Hydraulic Theory for more in-depth info). The problem is brake fluid is hygroscopic, which means it attracts and holds moisture from the surrounding environment. That moisture has a significantly lower boiling point which can cause a reduction or complete loss of braking ability if it vaporizes. To reduce the chance of this happening your brake fluid should be changed at least every 2 years (and should be included in a Service B), even if you have a classic car or other vehicle (motor home, motorcycle) that is driven only occasionally.

Why Time Matters More Than Mileage

This is one of the biggest misconceptions customers have.

Brake fluid absorbs moisture whether the vehicle is driven or not, which is why Mercedes specifies replacement based on time rather than mileage.

Some vehicles may require special equipment and procedures to replace the brake fluid, such as the Mercedes-Benz SBC system found on certain E (211), CLS (219), and SL (230) models. I use equipment that is capable of performing brake fluid replacement on these systems.