What you need to know about using and replacing brake fluids
What does brake fluid do in a vehicle?
Brake fluid is a hydraulic medium that transmits the force from the brake pedal to the calipers or wheel cylinders. It must withstand high temperatures and pressures without boiling or thickening.
What does DOT mean and what types of brake fluid are there?
A key term when it comes to brake fluids is the DOT specification. This standard, set by the U.S. Department of Transportation, defines minimum requirements for boiling point (dry and wet), viscosity, and chemical composition.
The most common types of brake fluid are:
DOT 3 / DOT 4: Glycol-based; older standard, commonly used in passenger cars and classic vehicles
DOT 4 LV: Glycol-based with low viscosity; suitable for ABS and ESP systems
DOT 5.1: Glycol-based with high thermal stability
DOT 5: Silicone-based; not compatible with glycol-based types
ISO 4925 Class 6: For vehicles with electronic brake systems, e.g. Eurol Brake Fluid DOT 4 LV
Important: Silicone and glycol-based brake fluids are not compatible. If mixed, the entire braking system must be replaced.
Key properties of brake fluid
A quality brake fluid must meet the following criteria:
High boiling point: Prevents vapor lock, which causes the brake pedal to feel soft or unresponsive
Low freezing point: Prevents freezing in cold conditions
Seal compatibility: Prevents leaks and damage to rubber components
Hygroscopicity: Absorbs moisture, which over time reduces performance
Why is the boiling point so important?
Brake fluid has two boiling points:
Dry boiling point: The temperature at which fresh brake fluid starts to boil
Wet boiling point: The temperature at which brake fluid boils after absorbing about 3.7% moisture
Since brake fluid absorbs moisture from the air, the boiling point drops significantly over time. This increases the risk of vapor lock and brake failure.
Brake fluid
Dry boiling point
Wet boiling point (after ±2 years)
DOT 3
± 230 °C
± 140 °C
DOT 4
± 260 °C
± 155 °C
DOT 4 LV
± 265 °C
± 170 °C
DOT 5.1
± 260 °C
± 180 °C
A low boiling point can lead to vapor lock, reduced braking performance, increased wear of the hydraulic system, and ABS/ESP malfunctions.
DOT 4 LV offers extra safety thanks to:
Lower viscosity at 40 °C (faster ABS/ESP response)
Higher wet boiling point (more reliable under load)
In heavily loaded vehicles, trailers, or when driving in mountainous areas, brake temperatures rise rapidly. Fresh brake fluid with a high wet boiling point is therefore essential.
When should brake fluid be replaced?
Timely replacement is critical. Due to its hygroscopic nature, brake fluid absorbs moisture, lowering its boiling point and increasing the risk of vapor lock. Aging occurs even in sealed systems.
Practical tips:
Always follow the vehicle manufacturer’s (OEM) recommendation
For intensive use (mountains, motorsport, heavy-duty equipment): replace more frequently
Use a boiling point tester if in doubt about fluid quality
How do you choose the right brake fluid?
Choose brake fluid based on:
OEM specification: This is leading. If DOT 3 or DOT 4 is specified, DOT 4 LV is also allowed due to its broader specification and higher thermal safety. The reverse is not true: DOT 3 or DOT 4 cannot be used in systems requiring DOT 4 LV.
Temperature and usage conditions: Consider mountainous terrain, heavy loads, or industrial applications.
System requirements: Modern vehicles with ABS, ESP, or torque vectoring require low-viscosity fluids. Eurol Brake Fluid DOT 4 LV meets ISO 4925 Class 6.
Which brake fluid for electric vehicles?
Some electric vehicles place lower demands on brake fluid, as they rely mainly on regenerative braking via the electric motor. This puts less strain on the hydraulic system. In these cases, DOT 3 is often sufficient. However, Eurol DOT 4 LV is also suitable.
Which brake fluid for rally and racing?
For high-performance braking systems in rally and racing, we recommend a specialized brake fluid: Eurol Specialty Racing Brake Fluid. This is used in WTCR, rallying, and EuroNascar.
Key characteristics:
Extremely high thermal stability
Superior wear protection
Suitable for torque vectoring systems
Torque vectoring distributes brake or drive force per wheel and requires a fast-responding hydraulic system. This places additional demands on brake fluid viscosity – ISO 4925 Class 6 is the right fit here.
