Brake fluid: when to change and why it matters

Brake fluid is “boring” until brakes get hot and the pedal starts feeling soft. The key point: most brake fluids absorb moisture. More moisture means a lower boiling point, and under heavy braking the fluid can boil and create vapor — the pedal sinks and braking force drops.

Why brake fluid degrades

Hygroscopic: it absorbs water from the air over time.
Boiling point drops: heat can create vapor → soft pedal → reduced braking.
Internal corrosion: moisture increases corrosion risk in lines, ABS module and cylinders.

Quick rule: if you don’t remember the last change, it’s probably time.

When to change

Normal use: about every 2 years (solid practice).
Hard use: mountains, towing, sporty driving, track days → more often.
After brake work: if the system was opened, consider refreshing/bleeding properly.

Symptoms the fluid may be past its best

Pedal gets soft when hot
Braking feel is inconsistent
Fluid looks very dark/brown (not a perfect measure, but a warning sign)

What fluid to use

Follow the manufacturer spec (DOT 3 / DOT 4 / DOT 5.1 etc.).
DOT 5 (silicone) is a special case — don’t swap “because it sounds better”.
Pick the right spec, not “higher number = always better”.

Keep brake work and fluids logged (date + mileage)