The boiling point of DOT 5.1 brake fluid is approximately 260°C (500°F) for dry boiling point and 180°C (356°F) for wet boiling point. DOT 5.1 fluid offers high performance in high-temperature conditions.
DOT 5.1 And DOT 4 Brake Fluid Boiling Points
| Feature | DOT 5.1 | DOT 4 |
| Dry Boiling Point (°C) | 260 | 230 |
| Dry Boiling Point (°F) | 500 | 446 |
| Wet Boiling Point (°C) | 180 | 140 |
| Wet Boiling Point (°F) | 356 | 284 |
| Recommended Use | High-performance vehicles, racing, extreme driving conditions | Standard vehicles, daily driving |
The boiling point is an essential factor in brake fluid performance because it determines the temperature at which the fluid boils and turns into vapor.
When brake fluid boils, it creates compressible gas bubbles in the braking system, leading to a spongy brake pedal and a significant reduction in braking effectiveness.
This is known as brake fade and can be dangerous in situations requiring heavy braking.
The dry boiling point refers to the temperature at which brand-new, unopened brake fluid boils.
As you can see from the table, DOT 5.1 boasts a significantly higher dry boiling point (260°C or 500°F) compared to DOT 4 (230°C or 446°F), so DOT 5.1 can withstand higher temperatures before boiling.
Over time, brake fluid absorbs moisture from the environment.
This water content lowers the boiling point of the fluid, which is known as hygroscopic absorption.
The wet boiling point represents the temperature at which brake fluid with a specific moisture content (typically around 3.5%) boils.
Even with absorbed moisture, DOT 5.1 maintains a higher wet boiling point (180°C or 356°F) compared to DOT 4 (140°C or 284°F).
With that said, DOT 5.1 is generally recommended for high-performance vehicles, racing applications, and extreme driving conditions where high heat generation is expected.
Its high boiling points offer a significant safety advantage in these scenarios.
However, for most everyday driving situations, DOT 4 is sufficient and provides a good balance between performance and cost.
Does DOT 5.1 Brake Fluid Affect ABS Performance?
No, DOT 5.1 brake fluid does not directly affect ABS performance.
ABS is a complex system that uses sensors, hydraulic pumps, and electronic control units to prevent wheel lock-up during braking.
Its primary function is to maintain steering control and stability, especially on slippery surfaces.
However, the type of brake fluid used in the system plays a small part in ABS operation.
Both DOT 5.1 and DOT 4 brake fluids are designed to be compatible with ABS systems.
But the key difference between the two is their boiling point.
DOT 5.1 has a significantly higher boiling point, making it more resistant to heat and vapor lock.
While this is beneficial for high-performance vehicles and extreme driving conditions, it doesn’t directly impact the ABS’s ability to function correctly.
Nevertheless, it’s essential to use the correct type of brake fluid recommended by your vehicle’s manufacturer.
Mixing different brake fluids can cause compatibility issues and negatively affect the entire braking system, including the ABS.
Always check your owner’s manual to determine the recommended brake fluid type for your car.