Rick's Free Auto Repair Advice

Check brake fluid — how to

How to check brake fluid

The anti-corrosion additives in brake fluid degrade over time and brake fluid accumulates moisture. That’s why brake fluid must be changed at periodic intervals.

Some carmakers recommend changing brake fluid every 2-years or every 24,000 miles, whichever comes first. Yet other carmakers don’t list any brake fluid change intervals.

Does brake fluid color matter?

NO. Color, by itself, is NOT an indication of brake fluid condition. You’ll see all kinds of color charts on the Internet that show brown fluid as needing replacement. There are NO laboratory tests to confirm that color has anything to do with brake fluid condition. NONE! Color as an indication of condition is a myth and it’s used to sell unnecessary brake fluid flushes.

In fact, you can change the brake fluid on a vehicle and it can turn brown within weeks after changing. Color change is due to the types of seals, assembly lube and rubber used in the system.

However, if you see debris in the brake fluid, that’s an indication of rubber component (seals and hoses) breakdown and the fluid should be changed and a full brake inspection completed.

Don’t let a shop convince you to get a brake fluid flush based solely on a brown or dark brown color of the fluid. Insist that they <strong>test it</strong>, or test it yourself with the items below. Here’s how you test brake fluid.

If you search online you’ll see several companies listing brake fluid color charts. There are no scientific studies to back up the claim that brown color has any bearing on brake fluid conditions. None. The only tests are moisture testers and brake fluid test strips. Period.

“Visual inspection of the fluid can be extremely misleading. The color of brake fluid can vary from clear to shades of blue. Even if the brake fluid is discolored or cloudy, it might still meet the system’s performance requirements. The brake fluid in the master cylinder reservoir can have a far different appearance than the fluid contained in the calipers. But, if you can see debris in the fluid with your naked eye, it could be a sign that rubber in seals or hoses are starting to degrade. Or, it could be the customer left the cap off the reservoir.”  — Andrew Markel Brake and Front End Magazine Oct 7, 2020

Check brake fluid for copper with test strips

Two-pack of Phoenxi brand brake fluid test strips to test the condition of brake fluid in a car or truck

Buy a package of brake fluid test strips and test your brake fluid so you don’t get scammed.

The presence of copper is a good indicator of the condition of brake fluid condition. As the anti-corrosion additives in brake fluid deteriorate, copper leaches into the brake fluid from the brazed tubing seam.  The high copper content in brake fluid is an indication that the fluid has lost its anti-corrosion effectiveness.

To avoid further system breakdown, brake fluid should be changed when the copper content is 200ppm (parts per million) or more.

Green color is an indication of high copper content.

You can do this test copper content yourself. Simply dip the brake test strip in the brake fluid reservoir, waits for 30-secs. and compares the strip color to a chart on the container.

Check brake fluid for pH

Brake fluid contains buffering additives to prevent corrosion. When the buffers wear out, the brake fluid becomes acidic and can damage internal components. A pH test strip can tell you whether the brake fluid has turned acidic.

Check brake fluid for moisture

Test the brake fluid’s moisture content with a battery-operated tester

Brake fluid moisture tester to determine condition of brake fluid in car or truck

Battery powered brake fluid moisture tester

or a  refractometer. If the fluid’s moisture content exceeds 2%, you should agree to a brake fluid flush.

Even if your maintenance manual recommends a periodic brake fluid flush based on time or mileage, it’s not a bad idea to have it tested before agreeing to the service. If the fluid hasn’t accumulated moisture and the copper content is low, you can extend the change intervals.

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©, 2021 Rick Muscoplat

Posted on by Rick Muscoplat


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