Brake fluid boiling point test

The brake fluid must have a high enough boiling point to avoid evaporation in critical parts of the brake system such as the disc and the brake drum. Vehicle deceleration is performed by friction in the brake units where enormous heating occurs. If the temperature of the brake unit exceeds the boiling point of the brake fluid, the fluid boils. The consequence of boiling causes difficult transmission of brake pressure and leads to failure of the brake system.

Moisture reduces the boiling point of the brake fluid. The higher the moisture content, the lower the boiling point. Up to 3% tolerates moisture content. For example, moisture-free DOT3 brake fluid has a boiling point of 205 °C, with 1% water 188 °C, with 2% 160 °C, while with 3% it will decrease to 145 °C.

The table below shows the boiling points for different types of brake fluid (DOT3, DOT4, DOT5, DOT5.1) for liquids without moisture and with 2% moisture content:

There are various devices for measuring the boiling point of brake fluid. So we have a brake fluid boiling point tester that shows the limit and measured temperature on the display, while the simplest testers via LED indicate whether the brake fluid is good or bad.

Brake fluid boiling point tester

To brake fluid boiling point test, follow these steps:

Preparation for measurement

Remove the cover and sieve from the brake fluid reservoir. Using a syringe, take some of the brake fluid from the reservoir and squeeze it into the measuring cup.

Boiling point measurement

Insert the saw probe into the brake fluid sample. Turn the tester on. Select the type of brake fluid and measure the boiling point.

Analysis of measurement results

Analyze the obtained value of the boiling point of the brake fluid. If the value is lower than allowed, replace the brake fluid. Turn off and clean the tester. Return the brake fluid sample to the reservoir. Close the tank with a cover.