What is Brake Fluid?
Brake fluid is a hydraulic liquid used in braking systems to transfer the force generated by pressing the brake pedal to the calipers, which then clamp onto the brake discs to stop the vehicle. This fluid is characterized by unique properties, most notably its high resistance to heat without boiling, and its incompressibility, which ensures precise and effective brake response under various driving conditions.
Why is Brake Fluid Important?
Brake fluid does more than just transmit hydraulic pressure. It performs several critical functions that help maintain system efficiency and driving safety, including:
1- Protecting brake system components from corrosion and rust
2- Absorbing heat generated by friction, helping preserve performance
3- Resisting boiling at high temperatures, preventing brake fade in extreme conditions
What’s the Difference Between DOT 3, DOT 4, and DOT 5.1 Brake Fluids?
Brake fluid types differ in their heat tolerance, moisture absorption rates, and compatibility with various braking systems. Key differences include:
DOT 3
- - Dry boiling point: approximately 205°C
- - Wet boiling point: around 140°C
- - Moderate moisture absorption
- - Suitable for regular driving in mild conditions
- - Compatible with DOT 4 and DOT 5.1
- - Loses about 25% of its boiling point when absorbing 3% moisture
DOT 4
- - Dry boiling point: approximately 230°C
- - Wet boiling point: around 155°C
- - Absorbs moisture faster than DOT 3
- - Preferred for mid-performance vehicles or hotter climates
- - Compatible with DOT 3 and DOT 5.1
- - Loses about 50% of its boiling point when absorbing 2% moisture
DOT 5.1
- - Highest boiling points: dry at around 260°C, wet at 180°C
- - Highest moisture absorption rate
- - Ideal for high-performance or heavy-use vehicles
- - Compatible with DOT 3 and DOT 4
How to Choose the Right Brake Fluid
Selecting the appropriate brake fluid requires considering several factors to ensure compatibility and optimal performance:
- Vehicle specifications: Always refer to the owner's manual for the manufacturer’s recommended type
- Driving conditions: For high-temperature environments or heavy loads, DOT 4 or DOT 5.1 is preferable
- System compatibility: DOT 5 is not compatible with DOT 3 or DOT 4
- Brand reliability: Choose a trusted brand for long-term performance and stability
How to Easily Check Brake Fluid Condition
Over time, brake fluid deteriorates due to moisture absorption and contamination, which affects braking performance. Regular checks are essential. Practical methods include:
Moisture Measurement
- Tool: Small electronic device with a probe
- Method: Dip the probe into the reservoir after warming the fluid slightly by driving
- Result: If moisture exceeds 3%, replace the fluid immediately
Electrical Conductivity Test
- Concept: Pure fluid doesn’t conduct electricity, but contaminated fluid does
- Method: Some devices measure conductivity to assess fluid quality
- Result: Low resistance indicates contamination and the need for replacement
Chemical Test Strip
- Tool: A strip that changes color based on fluid condition
- Steps:
- - Dip the strip into the fluid for a few seconds
- - Wait one minute and compare the color to the reference chart
- - Result: Significant color change indicates moisture or impurities; fluid should be replaced
Copper Content Measurement
- Background: Brake line corrosion releases copper into the fluid
- Method: Special test strips detect copper levels
- Result: If copper exceeds 200 ppm, it signals early corrosion and fluid replacement is necessary
Can You Mix Different Brake Fluid Types?
Mixing is not recommended, especially if the chemical compositions are incompatible.
When Should Brake Fluid Be Replaced?
It’s advisable to replace it every two to three years, or every 60,000 kilometers.
What Happens If Brake Fluid Runs Low?
Low brake fluid can lead to:
- - Reduced braking response
- - Warning light activation on the dashboard
- - Air entering the system, increasing the risk of brake failure