One of the most important fluid in your vehicle is brake fluid. It’s something that most people take for granted, until they have a spongy brake pedal, or even worse, spring a leak and have no brakes. Maintaining your brake fluid is essential for keeping your brakes operating properly and safely.
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Different Types Of Brake Fluid
There are 3 main types of brake fluids, DOT 3, DOT 4, and DOT 5. DOT 3 and DOT 4 are both hygroscopic fluids, meaning they absorb water. DOT 5 is a silicon based fluid, so it does not absorb water. When using DOT 3 or 4 brake fluid it is important to always use fluid from a sealed container, to be certain it isn’t contaminated.
Most cars and light trucks use DOT 3 or 4 brake fluid, with DOT 5 usually being used in higher performance or severe duty applications. This is due to the boiling point of the fluid. Brake fluid is under extreme hydraulic while the brakes are applied, increasing with brake pedal pressure. This pressure can create very high temperatures in the braking system. If the fluid begins to boil, the gas created in the system compresses, giving you less braking power, or no brakes at all. The boiling point of the brake fluid increases with each DOT rating, with 5 being the highest and 3 being the lowest.
Some European vehicles will use LHM fluid instead of those mentioned above. This is a mineral based oil, and sometimes doubles as fluid for active suspensions. So be certain to use the correct fluid for your application. This information is available in your owner’s manual and usually printed on the cap for the brake master cylinder.
What Color Is Brake Fluid?
Brake fluids come in a few different colors.
- DOT 3: Clear or amber
- DOT 4: Clear or amber
- DOT 5: Purple
- LHM: Green
What Color Is Brake Fluid When It Leaks?
If you have a low or spongy brake pedal there is a good chance that you have a leak somewhere in the brake hydraulic system. If you suspect a brake fluid leak, check the level in the master cylinder. If this is low, combined with a spongy or low brake pedal, check the brake lines, hoses, calipers, master cylinder, and wheel cylinders for leaks. Check along all the hydraulic components for leaking fluid, this will usually be a brown or black color. Because these parts are mostly located under the car, the contaminants on the outside will darken the brake fluid color. Although, in some cases it may still be clear or amber.
What To Do If You See Dark Brake Fluid?
If, while checking your brake fluid level or condition, you notice the brake fluid looks especially dark, it is a good idea to perform a brake fluid flush. Dark brake fluid could indicate that the fluid has been contaminated. This could be caused by the rubber components in your braking system breaking down internally, and the debris mixing with the brake fluid. Be sure to double and triple check the condition of all brake hoses, calipers, wheel cylinders, and the master cylinder. If in doubt it is always best to replace questionable brake components, as this could help avoid a possible loss of braking power. This could also be caused by the hygroscopic brake fluid absorbing moisture from the atmosphere.
How To Check The Color Of Brake Fluid?
Checking the brake fluid is a simple process. First, locate the brake master cylinder reservoir. This is usually located under the hood, near the firewall on the drivers side. Clean and remove the cap, then using a light look inside. If the fluid is clear or amber, you are probably just fine. If the plastic reservoir is discolored, you may need to remove some of the fluid to inspect the color. If the brake fluid is dark in color, perform a brake fluid flush.
When Do You Need To Replace Or Bleed The Brake Fluid?
Like most fluids in your vehicle, brake fluid has a service life and will eventually need to be replaced. Always follow the manufacturer’s recommendation for the service interval of a brake fluid replacement. If you have a low or spongy brake pedal, this could also be a sign that the fluid needs to be replaced. Be sure to check for fluid leaks and verify the condition of the other components in your braking system before performing a flush. Replacing old brake fluid with new brake fluid won’t make any difference if you have a collapsed brake hose or leaking brake line.
If you flush the brake fluid or replace a hydraulic component (line, hose, caliper, wheel cylinder, master cylinder), you will need to bleed the system. When you depress the brake pedal, it pushes brake fluid through the brake lines and forces pistons in your calipers or wheel cylinders to push pads or shoes against rotors or drums, forcing your car to slow down or stop. Brake fluid cannot be compressed, so it works very well in a hydraulic system. However, when you open the system, air is introduced. Air can be compressed, and while braking, the air is compressed and takes up space in the system. This doesn’t allow you to have full braking power and will result in a pedal that sinks to the floor instead of holding hydraulic pressure. Bleeding the system will remove the air from the system, restoring full braking power.
Is A Brake Fluid Leak Serious?
Brake fluid leaks are a very serious problem and safety concern. If you suspect or discover that you have a brake fluid leak, have it inspected and repaired immediately. Brake fluid leaks can result in low braking power or no brakes at all! Be sure to follow service information when repairing your braking system. Improper servicing can be extremely dangerous to you and anyone else on the road.