Brake Fluid Testing - How and Why To Test

Brake Fluid Testing FAQ

Brake fluid exchange – also known as a brake fluid flush – is one of the most important safety procedures you can do. When brake fluid is degraded it can severely reduce stopping power, the loss of which can have fatal consequences.


Yet despite its important role in the car’s mechanical function, brake fluid is not well understood, nor are the indications of when doing an exchange is called for. Right now millions of cars are cruising America’s roads in need of this critical procedure – and thousands of repair shops are missing an opportunity to provide this valuable service.

Our sincere hope is that by providing information about brake fluid testing we are helping repair shops better serve customers while strengthening their business.  You can read all of the questions below (if you would like) or you can take a look at our interactive training on BrakeStrip brake fluid testing by watching the videos below (if it is not already playing for you).

Q: What makes brake fluid exchange so important?
Over time, in the course of its normal life cycle, brake fluid becomes contaminated with various substances. Among these are copper particles that corrode into the fluid from the brake lines. Brake lines are made of steel, but use a copper lining to make them seamless. Once that contamination reaches a certain level, per MAP guidelines, the fluid must be changed to maintain the effectiveness of the brakes.

Q: Doesn’t brake fluid have corrosion inhibitors?
Yes, brake fluid is formulated with corrosion inhibitors, but those break down over time and corrosion begins to occur. The reasons the inhibitors break down include:
  • Heat from brake rotors
  • Undersized brake system
  • Stop and go driving
  • Thermal cycling
  • Low quality brake fluid
Q: What happens when corrosion inhibitors are depleted?
Once the inhibitors are depleted, corrosion occurs at an ever-increasing pace. The brake fluid becomes contaminated with particulates including copper from the brake lines and iron from active corrosion. Copper plating can damage ABS components and accelerates corrosion of the entire brake system. The presence of these particulates in the fluid can lead to damage of:
  • Caliper and wheel cylinder
  • Brake lines
  • Metering valve
  • ABS modulator
  • Master cylinder
Q: Can I detect contamination by the color of the brake fluid?
No! Once new (amber colored) brake fluid is installed in a vehicle, the color can darken rapidly due to contact with seals and hoses. Even brand new cars, never driven, can have dark fluid due to the color of brake system assembly lubricants used.

Q: What about moisture in brake fluid?
Interestingly, moisture is not the main contaminant that causes brake system problems, though thought to be the main problem by many industry professionals. Research by the Ford Motor Company indicates moisture contamination of brake fluid was approximately 1% in test vehicles that had been in service as long as 7 years. Moisture testing is recommended only for severe-duty vehicles.

Q: What does the government say about brake fluid service?
The National Highway Traffic Safety Administration (NHTSA) has published the following finding from an internal study:
“Internal corrosion does take place in the brake fluid over time. A prudent recommended practice to combat this situation would be to periodically exchange the brake fluid by completely bleeding the brake system and exchanging the old fluid with fresh fluid that meets current OE specifications.”

Q: How do you know when to “periodically” change brake fluid?
There is only one way… and that is to test it. Most service facilities don’t know when brake fluid was last serviced in a vehicle and since you can’t tell brake fluid condition by color, time or mileage, you’ve got to test it. The industry has adopted copper levels as the best way to determine when to “periodically” replace brake fluid.

Q: What is the Phoenix Systems BrakeStrip™?
BrakeStrip brake fluid testing is a 60-second test of the copper content of brake fluid. A BrakeStrip is inserted into the fluid and in one minute it changes color based on the level of copper. Holding the strip against a BrakeStrip reference chart provides easy-to-see visual evidence of the copper content of the brake fluid and indicates whether brake fluid should be replaced.

  • Is not a moisture test
  • Measures copper corrosion
  • Is repeatable – same result every time
  • The only test that uses MAP guidelines for brake fluid test results
Q: What does the industry say about BrakeStrip brake fluid testing?
Well, copper is the new standard for testing brake fluid.
  • NAPA named BrakeStrip™ as a key step in “The Perfect Brake Job”
  • The new MAP guideline requires brake fluid replacement at 200 ppm copper
  • BrakeStrip technology and its’ use is recommended or approved by: Raybestos, Bendix Brakes, U.S. Military and others
Q: Are there any tips or tricks to achieving a good brake fluid exchange?
  • Apply brakes a few times to suspend contaminants in brake fluid
  • Remove old brake fluid and contaminants from reservoir
  • Add new brake fluid to reservoir
  • Push and hold brake pedal 1 inch during entire procedure to allow special access to a chamber in the master cylinder
  • Pressure flush the system using the O.E. bleeding sequence and instructions
  • Allow 1 to 2 quarts of new brake fluid to pass through the system
  • Remove any trapped air with a Phoenix Systems Reverse bleeder, then test the brake pedal
Q: Why does brake fluid need to be replaced?
Over time corrosion inhibitors become depleted and brake components can be damaged by corrosion and contamination.

Q: Why test for copper and where does it come from?
Copper is the worst metal to corrode in the brake system. Copper is in the braising of steel brake lines.

Q: What's the big deal about copper?
Copper levels predict more damaging corrosion. Copper can also damage ABS components and accelerate corrosion of iron brake parts.

Q: Is there a brake fluid service standard?
Yes, The Motorist Assurance Program (MAP) has established that brake fluid replacement is required at 200 ppm of copper.

Q: What about moisture (water) in brake fluid?
No moisture standards exist and moisture is rarely an issue due to today’s EPDM brake hoses and sealed brake systems.

Q: Can you tell brake fluid condition by dirty color?
No, brake fluid turns dark mainly due to dye from the hoses and other components in the brake system.

Q: What about time or vehicle mileage?
The domestic OE manufactures say that the brake fluid should only be changed if it is proven to be contaminated.

Q: Is copper testing accepted by the California Bureau of Automotive Repair (BAR)?

Q: What do the brake manufacturers say about BrakeStrip?
A lot...Click on the logos below to read their endorsements of BrakeStrip.

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