though most owner’s manuals do not have a recommend interval for replacing brake
fluid having it replaced every 2 years does help minimize any potential brake system failure. There are a several
different ways to test brake fluid; one way is with chemical test strips,
strips are dipped in the fluid and change color they test for moisture content
as well as copper content and some even can tell the virtual age of the fluid.
Another way is with a refractometer moisture content is very visible because of
the refractometers prism design. Brake fluid testers, these measure the
electrical resistance of the fluid while some are designed to calculate the
fluids boiling point by actually boiling small samples.