A look at brake fluid testers... and an alternative approach

September 1, 2011 | By Richard Prince


Do you have any thoughts on or know of any reviews of brake fluid testers? I’ve seen two styles: test strips (Phoenix Systems FASCAR-1-100) and electronic (Jegs tester part number 80665).


Most of the electronic brake fluid testers measure the boiling point of brake fluid or its moisture content. The moisture content of the fluid is then used to interpolate its boiling point. Boiling point is one element among several that quantifies brake fluid’s effectiveness and safety.

In contrast, the test strips that you mention measure the copper content of the brake fluid. What is the relevance of copper particles in the fluid? That’s a simple question with a complicated answer.

With the widespread use of anti-lock braking systems beginning more than 20 years ago, certain problems arose that either didn’t exist or weren’t nearly as widespread prior to the introduction of anti-lock brakes.

These new braking system problems included diminished performance and component failures because of brake fluid contamination. Some of the reasons why anti-lock brakes are more susceptible to problems from corrosion and resultant contaminated brake fluid include higher fluid pressures, increased complexity of the ABS systems, and closer component tolerances.

In response to a noticeably higher number of problems with anti-lock braking systems, the National Highway Transportation Safety Administration (NHTSA) began examining ABS systems at its East Liberty, Ohio, Vehicle Research and Test Center in the 1990s.

Among other things, the NHTSA found what appeared to be corrosion deposits in the ABS hydraulic pressure control valves. Researchers suspected that this was the result of metallic components in brake fluid, so they requested that the National Institute of Standards and Technology (NIST) conduct some preliminary studies into the nature and scope of metallic corrosion in ABS brake systems.

The stated objective of this work was to help NHTSA, the automotive industry, and consumers by developing a better understanding of the corrosion phenomena in the ABS environment.

The corrosion scenario hypothesized to explain the observations initially made by NHTSA researchers is that the copper in the brake lines corrodes at a slow rate over several months or years resulting in copper ions in the brake fluid which then act as oxidizers and plate out in the ABS valves when the corrosion inhibitors in the brake fluid can no longer prevent corrosion of the ferrous components. (Though most automotive brake lines are steel, the steel tubing is manufactured from flat stock that’s rolled into a tube and then the seam is brazed with a copper brazing alloy, thereby putting the brake fluid in contact with a significant amount of copper.) The NIST and NHTSA studies suggest that over time degradation of brake fluid in normal service will lead to increasing concentrations of copper in the fluid and this copper can increase corrosion of other metals in the brake system. And that, in a nutshell, is what led to the development and marketing of test strips that can measure copper content in the fluid.

Not surprisingly, there is no love lost between the people who make and sell the copper test strips and the people who make and sell the electronic devices that measure moisture content and boiling point.

After reading a lot of the claims, counter-claims, assertions, accusations, and other ramblings of various constituents from both camps I came away with a mild headache and no clear conclusion. It seems likely to me that measuring copper content or moisture content can both be reasonably accurate techniques for evaluating the health of automotive brake fluid.

On the other hand, you can do what many, many people have done since the dawn of hydraulic brakes, which is skip the test gear and use common sense.

My personal choice is to change the brake fluid in any vintage car I buy soon after I buy it, and then change the fluid again when it changes color significantly, looks cloudy/dirty, when any brake service or restoration is done, or when several years have passed since it was last changed. Is this a waste of time and money? Maybe, sometimes, but on the other hand the electronic testers and test strips also cost money and whether and how effective and accurate they are can certainly be subject to debate.