Brake Fluid Test

Boiling-point testers heat a small sample and measure the actual boiling point. Simple pens estimate water content by measuring conductivity. Many workshops test the fluid at every service. Testing at the reservoir only shows the fluid there; fluid at the calipers can be in worse condition.

Water absorbed by the fluid changes its electrical properties and lowers its boiling point, which testers detect.

Cheap conductivity pens can be inaccurate and are only a rough guide. Replace the fluid if the test shows it is out of limits, regardless of age.