Your car's brake system is one of several hydraulic systems used in the automotive world. Pressing the brake pedal causes the fluid to flow through the pipes, starting from the brake pump and reaching the discs or drums, which slow down the car by exploiting friction. For the system to work properly, you will need to have enough liquid in the system, and this will also need to be in good enough condition to be able to do its job. Here's how to check brake fluid.
Steps
Method 1 of 2: Check the brake fluid level
Step 1. Open the hood of the car
This is best done when the car is stationary in a flat area and the engine is cold.
Step 2. Look for the brake pump
In most cars, this is located at the rear of the engine compartment, at the driver's seat. Above the pump itself is a reservoir.
Step 3. Check the fluid level in the reservoir
In newer cars, this is transparent and has two lines indicated for the maximum and minimum level; the fluid level should always lie between these two lines. Cars prior to the 1980s may have metal fuel tanks, so you will need to remove the cap (newer caps screw and unscrew, while older caps may need to be unclipped with a screwdriver).
Step 4. Add brake fluid to the reservoir as needed
Pour the fluid carefully and clean up any drips, because brake fluid is toxic and corrosive.
Only use brake fluid of the DOT specification listed in the car's manual. There are 3 main specifications: DOT 3, DOT 4 and DOT 5, each with its own characteristics. DOT 4 fluid can be used in some cars that use DOT 3 fluid (but never the other way around), while DOT 5 fluid can only be used in cars that require that type of fluid
Step 5. Close the tank and close the hood
- If the brake fluid is far below the minimum level, check the brakes, as there may be excessive consumption of them. As the brake pads wear out, brake fluid builds up inside the brake calipers.
- It can also happen that the brake reservoir is full but the fluid cannot reach the master cylinder. If the brake pedal feels "spongy" even after filling the tank, take the car to a mechanic.
Method 2 of 2: Check the condition of the brake fluid
Step 1. Check the color of the brake fluid
Under normal conditions, this is brown; if it is black or in any case very dark, it may need to be replaced (but other controls are needed).
Step 2. Dip a strip of chemical paper into the liquid
As brake fluid ages, additives to prevent corrosion lose their effectiveness. The check strips check for the presence of copper in the fluid - the more copper there is, the older the brake fluid will be. One such type of strip is the Phoenix Systems "BrakeStrip for Brake Fluid Test".
Step 3. Check the humidity level with an optical refractometer
Brake fluid is hygroscopic, meaning it absorbs moisture from the surrounding environment over time. This moisture dilutes it and lowers its effectiveness, leading also to the components of the braking system to corrode. After 18 months, the liquid may have absorbed about 3% moisture, which could lower the boiling point by 40-50%.
Step 4. Check the boiling point of the fluid with a suitable electronic device
The DOT 3 specification fluid must have the dry boiling point at 205 ° C and the boiling point after humidification at 140 ° C, while the DOT 4 must boil at 230 ° C when dry and at 155 ° C when wet. The lower the temperature at which the fluid boils, the less effective the liquid is.
