Without a proper brake fluid, safely stopping your car would be nearly impossible. Brake fluid move through a series of brake hoses and lines as a hydraulic liquid — a fluid passing through a confined space while yet under pressure. It sends the force of pushing on the brake pedal to brake calipers or drums to prevent the car’s motion.

Brake fluid is vital to the braking system and must carry out its duty under exacting conditions. According to the Department of Transportation’s National Highway Safety Administration(NHTSA), brake fluid must pass testing for 4 crucial standards:

Stay fluid at low temperatures; it must not solidify by freezing.
Resist boiling (and evaporating) at high temperatures.
Operate with other components of the brake system and other brake fluids.
Mitigate the brake system corrosion.
After brake fluid testing, all brake fluids are shown with DOT (for the Department of Transportation) and a number representative of a higher boiling point. Most vehicles in America use the hygroscopic DOT 3 or 4, which implies they will absorb moisture out of the air. Brake master cylinder reservoirs seem to be empty in case this starts to happen. They should not be opened except its absolutely necessary to keep premature degradation produced by the absorption of heat and moisture. While this happens naturally through braking, speeding up the process enhances the formation of rust and debris in the brake system — produced by the increasingly acidic brake fluid.



There are many different types of brake fluid: DOT 3, DOT 4, and DOT 5, as well as a few subcategories. Typically, the lower the number, the lower the boiling point.

DOT 3

DOT 3 brake fluids are glycol-based and are amber-colored. They have the lowest dry boiling point, implying their boiling point when new, followed by a rather low wet boiling point, or temperature at which the fluid boils when it is degraded.

Boiling Point: 401 degrees Fahrenheit

Degraded Boiling Point: 284 degrees Fahrenheit
Since DOT 3 is hygroscopic, it needs replacement every few years to preserve effectiveness.

DOT 4

European vehicle makers use mostly DOT 4 brake fluid. Though equally glycol-based, it processes a higher boiling point from borate-ester additives that lowers the acids formed by absorbed moisture. DOT 4 often costs twice as much as DOT 3 to cover the extra chemicals. They function better than DOT 3 fluids in their early life, but their boiling point ends up dropping rapidly in later stages.
Read More:https://automobileglobe.com/what-are-the-different-types-of-brake-fluid/