What brake fluid does
Brake fluid transfers pressure from the pedal to the brakes at the wheels. It must retain the correct properties in everyday driving and under high thermal load. It is part of a safety-critical system, so both the fluid and the replacement procedure must follow the specification for the particular vehicle.
Why brake fluid ages
Common brake fluids gradually absorb moisture. This changes their properties and can reduce the margin against boiling during repeated or prolonged braking. Condition cannot be judged reliably by colour alone; the service history, the correct specification and professional testing where appropriate also matter.
How often to replace it
There is no single interval that applies to every vehicle. Use the service schedule or owner's manual for the specific car; on many vehicles replacement is time-based rather than mileage-only. If the history is unknown, have the fluid and brakes inspected and decide the next step from the manufacturer's information and the inspection result.
Why topping up is not enough
A falling level may be linked to pad wear, but it can also indicate a leak. Topping up does not restore the properties of old fluid or remove the cause of the loss. If the level is near MIN, a brake warning appears or the fluid repeatedly drops, the vehicle needs an inspection; do not continue driving with an empty reservoir or a visible leak.
When to stop and stop driving
Stop safely if a red brake warning appears, the pedal feels unusually soft or sinks, braking performance has weakened, the car pulls strongly while braking or fluid is visibly leaking. Continuing may be dangerous. Also follow the vehicle handbook and arrange recovery if you are unsure.
What a workshop checks
The inspection covers fluid level and condition, the tightness of pipes, hoses and connections, and wear elsewhere in the braking system. Replacement uses the specified fluid and the system is bled correctly. At MotPro in Prague 9 we first assess the vehicle and agree the scope of work with you in advance.
Every vehicle and fault is different. This article provides general guidance; an inspection of the specific vehicle determines the correct procedure.