Why Test Fluids?
Why test the boiling point?
Brake fluid is hygroscopic, readily absorbing water from the atmosphere, which changes the characteristics of the fluid. Among these changes is the boiling point, a direct indicator of the amount of water moisture present. Thus by testing for boiling point the heat resistance condition of the brake fluid can be determined. Tests can be performed as often as required to ensure that the brake fluid in question meets U.S. Federal Safety Standards, and standards of other respective countries that use the Jerco Quality Tester.
Brake Fluid Boiling Characteristics
Graph 1 depicts the temperature profile of the ERBP (Equilibrium Reflux Boiling Point) of brake fluid as a function of percent added water content. As shown, the boiling point temperature varies inversely with the water content. The dry boiling point of DOT-3 brake fluid is around 495 degrees Fahrenheit and drops to approximately 280 degrees with 5 percent water. The dry boiling point of DOT-4 brake fluid is around 515 degrees Fahrenheit and drops to approximately 330 degrees with 5 percent water.
Graph 2 shows the effect of temperature versus time as the fluid is heated to boiling. Here the fluid temperature rises steadily until it reaches a constant boiling temperature. This graph shows the boiling point curves of two separate brake fluid samples, dry (less than 0.1% water) and with roughly 1% water added. As shown, the brake fluids come to a steady-state ERBP (Equilibrium Reflux Boiling Point) after approximately 5 minutes of testing. The fluids then boil at a constant temperature for the balance of the 10 minute test cycle.
This graph visually shows the degrading effect of water absorption and the lowering of the brake fluid's boiling point quality. The graph also shows the capability of the JERCO Boiling Point Tester to evaluate a brake fluid's quality by testing and measuring the boiling point.