Brake fluid, also known as hydraulic brake fluid, is a functional liquid used in vehicle hydraulic braking systems to transmit pressure, enabling wheel brakes to function. It primarily serves roles in energy transfer, heat dissipation, rust/corrosion prevention, and lubrication. With advancements in automotive technology, brake fluids have evolved from castor oil-based and mineral oil-based types to fully synthetic formulations. Modern standards encompass over a dozen physicochemical and bench-testing criteria, with critical attention required to the following five parameters during sales and usage:

Key Parameters and Performance Indicators

1. Equilibrium Reflux Boiling Point (ERBP)

   • The boiling temperature measured under standardized dry conditions, reflecting the high-temperature resistance of fresh brake fluid. Higher ERBP values indicate better high-temperature performance.
   • Requirements:
     • HZY3: ≥205°C | HZY4: ≥230°C | HZY5: ≥260°C | HZY6: ≥250°C
     • For most passenger vehicles (HZY4), replacement is recommended when ERBP drops below 170°C.

2. Wet Equilibrium Reflux Boiling Point (WERBP)

   • The boiling temperature measured after the fluid absorbs moisture, simulating real-world usage. Higher WERBP values ensure stable performance in humid conditions.
   • Example: DOT5.1 brake fluids typically achieve WERBP >180°C.

Common Brake Fluid Types and Performance Comparison

DOT5.1 Advantages:

• Superior moisture resistance, high ERBP/WERBP (>260°C dry, >180°C wet), and oxidation stability.
• Compatible with DOT3/DOT4 systems, ideal for harsh conditions (e.g., frequent braking, mountainous terrain).

TONIC Kinetic DOT4+HD:

• Synthetic formulation with ERBP ≥260°C and WERBP >160°C, comparable to DOT5.1 for track/performance use.

Consequences of Delayed Brake Fluid Replacement

1. Corrosion: Hygroscopic properties lead to water absorption, corroding metal components (e.g., calipers, master cylinder).
2. Vapor Lock: Moisture lowers boiling points, causing fluid vaporization under heat and resulting in spongy brakes.
3. Blockages: Contaminants (e.g., sludge, particles) accumulate, impairing hydraulic pressure transmission.

When to Replace Brake Fluid?

• Symptoms:
  • Uneven braking force or extended stopping distances.
  • Soft brake pedal feel (indicative of air bubbles).
• Testing: Measure moisture content (≥3% water indicates replacement urgency).

For real-time updates on automotive standards or compatibility queries【TERZO】