The importance of keeping your brake fluid in good condition cannot be over emphasised, and it is not an exaggeration to say that it is the single most important fluid in any vehicle. How well the brakes work depends entirely how clean, fresh, and free of water and other contaminants your brake fluid is, which is why it is vitally important to check your brake fluid at least once a week. So what do you look for when checking the brake fluid? Read on and we will explain the issues.
Check the Level
On most cars, the level of the brake fluid will be visible through the translucent plastic of the reservoir, on which the correct level will be clearly marked. Over filling the reservoir causes leaks, but more importantly, spilled brake fluid will eat through the paint of the engine compartment.
A small, gradual drop in the brake fluid level is normal, and is caused by the normal wear of the brakes, but a sudden drop indicates a leak. Leaks can be in one, or several places, such as the rear wheel cylinders, ruptured pipes, or out of the back of the master cylinder where it attaches to the brake booster.
All brake fluid leaks are potentially dangerous, which requires that they must be investigated and corrected without delay to prevent unexpected brake failure.
Check the Color
Fresh brake fluid is either straw or amber in color and while some types, such as DOT 5, or Dot 5.1 fluid can be purple in color, these formulations are not usually used in normal production vehicles.
Over time, brake fluid absorbs water from the atmosphere, which can change the color to dark yellow, light brown, or even black. Other causes of discoloration are contamination by mineral engine oil, or the wear particles of moving rubber seals in the master cylinder. Brake fluid in this condition is dangerous, and the entire brake system needs to be flushed to purge the contaminated fluid from the system.
However, while it is possible to flush the brake system on a DIY basis, the procedure is best left to a competent repair shop due to the extreme complexity of many modern brake systems. Making a mistake could allow air to enter the system which might be impossible to remove by traditional bleeding methods.
The best way to purge brake systems is by extracting the brake fluid with a vacuum, which precludes the possibility of air entering the system if the procedure is carried out correctly.
How to Spot Brake Fluid Related Problems
The first sign of contaminated brake fluid is excessive pressure required to stop the vehicle. This could of course also be caused by vacuum issues, but in the case of brake fluid, the pedal will have a soft, or “spongy” feel.
This is caused by the presence of water that boils as the brake fluid heats up, and there is no remedy for this other than a complete brake fluid replacement. Other signs of degraded brake fluid could be:
- Excessive pedal travel due to the presence of water in the fluid.
- Increased stopping distances. There are many caused of this, but if the brake fluid is discoloured in combination with longer stopping distances, replacing the brake fluid will restore the brakes to full efficiency.
Can I Mix Different Brake Fluid Types?
The short answer is NO. Brake fluids with DOT 3 and 4 designations consist of glycol bases to which a package of additives is added. These additives are meant to provide lubrication of moving parts, as well as prevent corrosion, but generally, these types of brake fluid are fully compatible.
However, brake fluid with DOT 5 and 5.1 are based on silicone, and while they do not absorb moisture, they are significantly more compressible than DOT 3 and 4 types, and they can, and must only be used in systems that are designed specifically for them. Typical applications would be on race cars, and other systems that work at higher temperatures than those encountered on normal production vehicles.
Adding DOT 5 brake fluid to your system will at the very least lead to increased stopping distances, as well as having to apply more pressure on the brake pedal than normal.
How to Store Brake Fluid
Brake fluid should never be stored for longer that it would take to get the job of replacing it done. Brake fluid can absorb water from the atmosphere even in sealed plastic containers since most plastics are permeable to water in varying degrees, so if you have container of brake fluid that is older than a few weeks, discard it.
Only purchase brake fluid in the quantities you require immediately, and never use brake fluid from unsealed container because there is no telling how much water it contains. If you absolutely must store brake fluid for any length of time, only purchase brake fluid in metal containers. Metal is the only material that provides adequate protection against water absorption, but even so, do not use the brake fluid if the container had been left unsealed even for a few hours. Water is brake fluid’s greatest enemy, and if you allow contamination to take place, the water in the brake fluid will without any doubt be your greatest enemy as well.