While brake fluid is technically a type of hydraulic fluid, it is a specialist fluid designed specifically for vehicle braking systems and should generally not be used as a substitute for other types of hydraulic fluid.
Understanding the distinction is crucial for system performance and longevity.
What is Hydraulic Fluid?
Hydraulic fluid is a non-compressible fluid used in hydraulic systems to transmit power. When pressure is applied to the fluid in one part of the system, that pressure is transmitted through the fluid to another part, enabling work to be done (like lifting a heavy object or applying a brake).
Common applications for hydraulic fluid include:
- Industrial machinery
- Construction equipment
- Aircraft hydraulics
- Power steering systems
- Vehicle braking systems
Why Brake Fluid is Different (Even Though It's Hydraulic)
As highlighted in the reference, Brake fluid is generally a specialist hydraulic fluid tailored for this exact use. This means it has unique properties specifically engineered for the demands of a braking system:
- High Boiling Point: Braking systems generate significant heat due to friction. Brake fluid must have a very high boiling point to prevent vapor lock, a dangerous condition where the fluid boils and creates compressible gas bubbles, leading to brake failure.
- Specific Viscosity: It needs to maintain a consistent viscosity across a wide range of temperatures to ensure reliable performance in hot and cold conditions.
- Corrosion Inhibition: Brake fluid contains additives to protect the metal components within the braking system from corrosion.
- Material Compatibility: It is designed to be compatible with the seals and components (often made of rubber or specific plastics) found within brake lines, cylinders, and calipers. Different types of brake fluid (like DOT 3, DOT 4, DOT 5.1) have varying compositions and compatibility requirements.
The Risks of Using Brake Fluid for General Hydraulic Applications
Using brake fluid in a system not designed for it, even though it's a hydraulic fluid, can lead to significant problems:
- Incompatibility with Seals and Materials: Brake fluid's composition, particularly its additives, can degrade or swell seals, hoses, and other components in hydraulic systems not built to handle it. This can cause leaks and system failure.
- Different Viscosity Requirements: General hydraulic systems might require fluids with different viscosity characteristics for optimal operation or lubrication. Brake fluid's specific viscosity might not be suitable.
- Lubrication Properties: While brake fluid provides some lubrication, it may not offer the same level of lubrication required by components (like pumps or valves) in other hydraulic systems.
- Additive Conflicts: Additives in brake fluid could react negatively with additives or materials in another hydraulic system.
In summary: Just because small bottles are available at every auto store doesn't mean brake fluid is a universal substitute. The application and fluid properties are quite precise for braking systems.
Example
Imagine a tractor's hydraulic system used to lift heavy implements. This system likely uses a standard hydraulic oil or a specific tractor hydraulic fluid designed for high pressure, lubrication, and compatibility with the system's seals and pump. Using brake fluid in this system would likely damage the seals, cause leaks, and potentially harm the pump due to insufficient lubrication and incorrect viscosity.
Conclusion
Always use the type of hydraulic fluid specified by the manufacturer for any given system. While brake fluid is a hydraulic fluid, its specialization for braking systems makes it unsuitable for general hydraulic use.
