Brake fluid is a corrosion-resistant hydraulic fluid that converts the force applied to the brake into relieving pressure in the car’s braking system.This oil is chemically stable and compatible with brake system components and is the best example to show the effect of Pascal’s law in real life. The role of brake fluid in the relationship between the hydraulic brake system and car movement is relatively simple. Brake fluid, as an incompressible fluid, transmits the force applied on the brake pedal to the front and rear brakes of the car by transferring pressure. The steps of car stopping are as follows:
Brake fluid is a corrosion-resistant hydraulic fluid that converts the force applied to the brake into relieving pressure in the car’s braking system.This oil is chemically stable and compatible with brake system components and is the best example to show the effect of Pascal’s law in real life. The role of brake fluid in the relationship between the hydraulic brake system and car movement is relatively simple. Brake fluid, as an incompressible fluid, transmits the force applied on the brake pedal to the front and rear brakes of the car by transferring pressure. The steps of car stopping are as follows:
- Pressure applied on the brake pedal
- Transferring force to the piston in the master cylinder
- Forcing brake fluid through the main cylinder and carrying it to the cylinder and wheels. (Being under the pressure of the brake fluid cylinder and transferring it to the wheel cylinders and calipers).
- Hydraulic pressure on the pistons to produce force
- Force transferring on pads with brake drum or rotor
- Finally, creating friction and slowing down or stopping the rotation of the wheels
Most brake fluids are hygroscopic (the ability of a substance to absorb water molecules from the surrounding environment and retain them), meaning that they not only lubricate all the moving parts and components of the car’s braking system but also absorb any moisture to prevent corrosion and rust.
Knowing what brake fluid does and how it contributes to the system’s function begins with knowing brake fluid and its types. Here are some properties of the brake fluid:
- Toxic and burning fluid
- Incompressible
- Non-freezing at low temperatures
- Fast paint remover
- Ability to absorb moisture
- High boiling point (too much heat applied to the brake fluid during braking)
- Appropriate viscosity at the low temperature to flow in pipes and paths
- Wide range of working temperature
- Very low volatility
- Compatibility with the equipment, components, and sealing parts of brake system such as o-rings, washers, etc.
The three main types of brake oil are:
1- DOT 3 brake fluid
The most common type of brake fluid is based on glycol, containing glycol ethers and additives to prevent corrosion (prolong the life of brake components) and increase lubrication (make the seals last longer). The oil color ranges from transparent to amber, and it absorbs moisture, reducing its boiling point and finally bringing it to the wet boiling point or even lower. Like all glycol-based fluids, it can damage the car’s paint.
- Dry boiling point of 401 degrees Celsius
- Minimum wet boiling point of 284 degrees Celsius
2- DOT 4 brake fluid
DOT4 brake fluid is similar to DOT3 but contains 20-30% borate ester, significantly increasing its boiling point. The oil’s higher wet and dry boiling point cause it to absorb less moisture. The higher boiling point means that the moisture absorbed by DOT4 cannot be drained and causes the additives of DOT4 oil to break down faster than those of DOT3. The price of DOT4 brake fluids is usually twice DOT3 due to the presence of more additives that make them perform better than DOT3, but over time, their boiling point decreases rapidly.
- Dry boiling point of 466 degrees Fahrenheit (°F)
- Wet boiling point of 311 degrees Fahrenheit (°F)
- The higher wet and dry boiling point of DOT4 makes it more suitable for more difficult applications.
3- DOT5 brake fluid
This type of brake fluid is silicone-based, often called synthetic brake fluid, meaning it does not absorb moisture.
The purple color of DOT 5 usually distinguishes it from other brake fluids. The boiling point of this oil is high, but it does not perform well in some brake systems due to making water foamy and forming air bubbles. Due to the lack of moisture absorption, it immediately repels any liquids that flow into the system. Moisture introduced into a brake system with DOT 5 fluid does not mix with the brake fluid. It causes the moisture to freeze or boil at inappropriate temperatures, leading to brake fade. This product is usually used in classic cars and cars that need non-petroleum brake fluids.
• Dry boiling point of 500 degrees Fahrenheit (°F)
• Wet boiling point of 356 degrees Fahrenheit (°F)
In general, brake fluid should be tested for four standards:
- To remain fluid at low temperatures and not to be hardened by freezing
- To resist boiling and evaporation at high temperatures
- To cooperate with other parts of the brake system and other brake fluids
- To resist the brake system corrosion
Without brake fluid, there will not be enough pressure to bring the vehicle to a complete and safe stop. Therefore, any unceasing fluid leakage for a while can cause problems on the road if not addressed.
The cause of reduced brake fluid in the engine
A decrease in brake oil can be the main factor indicating a problem in the car system. It is worth mentioning that several factors are influential in occurring this case, some of them mentioned below:
- Wear of brake pads
- Leakage in the brake system
- Brake pipe leakage:
- The burning smell of pads:
Time to check or change brake oil
- Turning on the brake warning light
- Stiff brake pedal and reduction of braking power
- Unusual sounds from the brake system
If you see any of these signs, you should quickly check your brake fluid level and, if necessary, bring it to the desired level. Also, if you suspect a leak in your brake system, you should visit a qualified mechanic to check and repair it.