Brake Fluid: The Flush Most People Skip

Here's a maintenance item that almost nobody does on time: brake fluid flush. Most manufacturers recommend every 2-3 years regardless of mileage, but it rarely shows up on quick-lube menus and many owners have never done it.

Why brake fluid goes bad

Brake fluid is hygroscopic — it absorbs moisture from the air through microscopic pores in rubber hoses and seals. Fresh DOT 4 fluid has a dry boiling point around 446F (230C). After two years of moisture absorption, that can drop to around 311F (155C) — the DOT 4 wet boiling point floor. Hard braking generates serious heat, and if your fluid boils, you get vapor bubbles in the lines. Vapor compresses — hydraulic fluid doesn't. That's how you get a pedal that goes to the floor.

How to check

• Brake fluid test strips cost a few dollars and measure moisture content — dip one in the reservoir
• Color check: fresh fluid is clear to light amber. Dark brown or black fluid is overdue
• If your pedal feels spongy or has more travel than it used to, contaminated fluid is a likely culprit

Why it matters

Beyond the safety issue of reduced braking performance, moisture in brake fluid corrodes internal caliper and master cylinder components from the inside out. A $100 fluid flush now prevents a $600 caliper rebuild later.

Quick action

Check your brake fluid reservoir — pop the cap and look at the color. If it's dark brown or you can't remember the last flush, put it on your list. This is a great DIY job with a $20 one-person bleeder kit.