Brake fluid provides hydraulic pressure to actuate your brake system’s pistons and provide braking. Here’s why, how, and when to perform a brake fluid change.
HOW IT WORK
Brake fluid conducts the hydraulic pressure that stops the vehicle. This “incompressible” fluid operates in a high-pressure, hot environment—100 to 200 degrees at normal operating conditions. Ever “smelled” your brakes on a long, steep downhill drive? If so, you may have been looking at closer to 550 degrees.
Brake fluid has a high boiling point, as boiling would transform the fluid into a gas and could lead to brake fade or failure. Unfortunately, brake fluid is hygroscopic, meaning it attracts and absorbs water from the atmosphere. Water in brake fluid will boil at a much lower temperature and can corrode brake components.
When to perform a brake fluid change
Change brake fluid if the pedal feels “spongy,” or if the brake lines are ever opened up during service. Examine the brake fluid—it should be yellowish and translucent. If it looks dirty or contaminated, it’s probably due for a change.
Avoid brake fade caused by contaminated brake fluid. Don’t regularly open the reservoir to check the brake fluid level. Doing so introduces air and moisture into the system. The clear reservoir has MAX and MIN lines for monitoring fluid levels without removing the cap. Never add brake fluid from a previously opened container.
About brake fluid types
Brake fluid is available in different types, specified as DOT 3, 4, 5, and 5.1. In general, the differences between the types are related to the fluid’s viscosity and boiling points. Braking generates a lot of heat—heat that’s transferred to brake fluid. Boiling points are important because if your brake fluid boils during extreme braking, air will be introduced into the system and brake failure will result. A good rule of thumb is to follow the vehicle manufacturer recommendations for which brake fluid to use, and know that brake fluids aren’t generally interchangeable, particularly DOT 5 which is silicone-based while the others are glycol-based.