Bendix High Performance DOT 3 & DOT 4 Brake Fluid Testing

As part of the Bendix Test Pilot Program, Ben, a mechanic at Heasman Steering shows how to test your brake fluid with the proper tools, in the correct way. "When it comes to testing brake fluid, it’s vital to understand the different types of brake fluid ratings and the testing equipment required to accurately test it."

Brake fluid is designed with a high boiling point to withstand the extreme temperatures generated during braking and needs to be checked to ensure it meets the exact temperature requirements.

DOT 3 and DOT 4 Brake Fluids are hygroscopic fluids that will absorb moisture when exposed to air. This occurs in instances such as opening the reservoir cap or through brake lines where the moisture level can build up over time. Brake fluid is designed to absorb moisture to prevent it from pooling and causing corrosion on metal components (see Figure 1 & 2 below). This is the normal process of the brake fluid’s life-cycle so we need to check that the moisture is at safe levels. Elevated moisture levels reduces the boiling point and effectiveness of the brake fluid (Figure 3). In hot weather conditions or in a vehicle that is experiencing heavy braking, the moisture can vaporize causing a vapor lock in the system (Figure 4). The vapor is compressible and prevents the solid hydraulic lock that fresh brake fluid delivers leading to a soft brake pedal or even complete brake failure.

When Bendix DOT 4 brake fluid is new, it has a high dry boiling point. As the moisture content builds to 3% in the brake fluid, it develops what is known as a wet boiling point of 155°C. This temperature is critical and the brake fluid must be replaced if the boiling point is below 155°C.

So how do we test the brake fluid to know if it requires changing?

There are 2 common tools used to test brake fluid. One is a conductivity tester, the other is a boiling point tester.

Bendix does not recommend using a conductivity tester as they have been known to fail when testing freshly opened brake fluid. Conductivity testers estimate the moisture content by converting the conductivity into an estimated boiling point. Since brake fluids vary from formula to formula, this test is not an accurate result unless the tester is calibrated to the manufacturer’s product when new.

Bendix recommends a tester that heats the brake fluid to determine the correct boiling point. Using a boiling point tester is the only accurate way to test brake fluid performance.

It takes less than a minute to measure the boiling point and confirm if the brake fluid has absorbed too much moisture to be safe. In the case on the following page, our wet boiling point is (155-200°C) which is above the Bendix DOT 4 minimum wet boiling point of 155°C. It’s important to remember that the system will continue to absorb moisture before the next service so it is recommended to change brake fluid regularly to ensure the vehicle is safe. By regularly checking your customers’ brake fluid condition is not only a vital safety issue but also a way of increasing your servicing revenue.

We used the AutoStop Brake Fluid Tester with its ergonomic design and user friendly features. It operates off the 12 volt supply from the vehicles own battery and the LCD display screen leads the operator through the complete test sequence. AutoStop Brake Fluid Tester is ideal for testing Bendix DOT 3 and DOT 4 brake fluids as well as racing fluids.

SEE IT IN ACTION! To watch the video, click here!

A boiling point tester is easy to use and takes less than a minute to record an accurate result.

If testing indicates the brake fluid needs to be replaced, get optimum performance from the hard working formula of Bendix High Performance DOT 3 & DOT 4 Brake Fluid.

Bendix DOT 3 & DOT 4 Brake Fluid is a high performing Polyglycol type fluid designed for optimum performance of hydraulic & conventional brake systems, and is available in 500mL and 4L bottles and 20L drums.

For more information on Bendix Brake Fluid, click here!