Generally speaking, most of us don’t look forward to spending money on car maintenance. Often the questions that come up are not only “Is it necessary?” but also “How often do you need to flush brake fluid?” – and most basic “Why?”

Let’s start with why. Brake fluid is an often overlooked, but vitally important part of your brake system that allows force to be multiplied. This, in turn, allows light to medium pressure from your foot to stop your 3000+ pound car moving at hi-way speeds. Pretty cool when you stop to think about it. I will include some links at the bottom of the page if you’re interested in more techy stuff about hydraulics.

Here are the basics of hydraulic brake system.

Brake fluid has a couple of jobs, to transfer and multiply energy and lubricate moving parts. It has two main enemies: moisture and heat.

Energy cannot be lost – only converted, therefore the basic physics of braking are convert forward movement (kinetic energy) into heat and dissipate the heat. This is done by the brake pads and rotors.

Brake fluid is a special fluid with a high boiling point that will not compress. Normal Dot 4 fluid, that is dry (uncontaminated with moisture) has a boiling point of over 400 degrees f. Unfortunately, brake fluid is also hygroscopic – meaning that it attracts moisture. Not a problem here in the northwest, right? The boiling point of Dot 4 “dry” is 446 deg. F. as little as 3.7% moisture content (wet) reduces the boiling point to 311 deg. F.

Heat from braking causing the rotors to glow red hot!


Brake fluid deterioration comes from several directions. Rubber parts in the master cylinder, wheel cylinders and calipers deteriorate and little flakes of rubber end up in the fluid. If the system has ABS (Anti-lock Braking) these little pieces of debris can get caught in the valves of the ABS unit and cause an expensive failure there. Heat will, over time, break down the fluid.  Then there is the moisture issue which not only lowers the boiling point, reducing braking efficiency but also allows the systems metal parts to rust which leads to premature failure.

So, is it necessary? YES!  Then “How often?” is the next question.


Here at London’s Automotive our goal is to prolong the life of your vehicle and lower the life time operating cost. Corrosion and rust internal to the brake system can turn a $200 brake job into a $600+ if it requires calipers and/or wheel cylinders.

A good rule of thumb is to replace the brake fluid (flush) every 30,000 miles or 2 years to maintain optimal efficiency.

The brakes are the most powerful system in your vehicle, more powerful than the engine! If your brake pedal feels soft or overly hard or just doesn’t feel “right”, give us a call and we will schedule you in for a brake system inspection. 541-753-4444


Here are those additional links I mentioned;

Pascal’s Law:

Pascal’s Principle and Hydraulics:

More on Disc Brakes: