Testing of brake fluid for the presence of moisture can be measured with a multimeter. The maximum permissible moisture content in the brake fluid is 3%. Over this value, it is necessary to replace the brake fluid because the braking efficiency is reduced. By measuring the voltage as a galvanic reaction of the brake system, the water level in the brake fluid is determined.
Testing brake fluid with a multimeter
Most vehicle manufacturers use a combination of different metals to make the braking system, aluminum in the pistons and housings, and steel in the brake lines and cylinders on the wheels. When moisture mixes with the brake fluid, a galvanic reaction (corrosion) occurs. The higher the moisture content in the brake fluid, the greater the corrosion and the stronger the galvanic reaction. A voltmeter measures the galvanic reaction voltage in the braking system. The magnitude of the measured voltage depends on the moisture levels in the liquid. The higher the percentage of moisture, the higher the voltage.
To testing brake fluid with a multimeter, follow these steps:
Preparation for measurement
Remove the brake fluid reservoir cap. Adjust the multimeter to measure direct voltage (DC). Connect the red cable to the plus/voltage connector and the black to the minus/common connector of the multimeter.
Voltage measurement
Place the tip of the red measuring probe in the brake fluid, and connect the black one to the unpainted part of the metal housing of the master brake cylinder. Wait for the measured voltage value to calm down.
Testing analysis
Analyze the measured voltage value. Voltages up to 0.3V indicate that the percentage of moisture in the brake fluid is lower than allowed. However, when the measured voltage is higher than 0.3V, it means that there is too much moisture and that the brake fluid must be replaced.
See also
Video recommendation
