Brake Fluid Color, Clarity & Smell: How to Check
Checking your brake fluid regularly is one of the most important maintenance tasks to ensure the safe operation of your vehicle. Maintaining the proper level and condition of brake fluid is critical because it serves as the hydraulic fluid that transmits force to your brake calipers, allowing you to slow and stop your vehicle.
Over time, brake fluid can become contaminated through absorption of moisture from the air. Heavily used and high-heat brake fluid also gradually breaks down. Contaminated and old brake fluid leads to a loss of braking performance, longer stopping distances, and potential brake failure. That’s why routinely checking the level, color, clarity, and smell of your brake fluid is essential to avoid safety risks.
This article will cover everything you need to know about inspecting your brake fluid. We’ll discuss what to look for when checking brake fluid properties and how to identify potential issues. We’ll also provide steps on how to change your brake fluid when needed.
What is Brake Fluid?
Brake fluid is a hydraulic fluid used in vehicle brake and hydraulic clutch applications. It is a high boiling point liquid that transfers pressure from the master cylinder to the brake caliper or wheel cylinder to slow or stop the vehicle.
Brake fluid is formulated primarily from glycol ethers and polyglycols to achieve a high boiling point and low viscosity. It has anti-corrosion properties to protect the brake system components. Brake fluid should be able to absorb the water that inevitably seeps in over time without reducing boiling point or damaging metal components.
The primary purpose of brake fluid is to transfer force quickly and evenly to all four wheels, provide consistent braking power, and resist overheating. High quality brake fluid is essential for safe, reliable braking performance.
Checking Brake Fluid Level
Checking the brake fluid level regularly is an essential part of maintaining your vehicle’s braking system. The brake fluid reservoir is typically located under the hood, near the firewall on the driver’s side. It will be a translucent plastic reservoir with minimum and maximum level lines marked.
The level should always be between the MIN and MAX lines – if it falls below the MIN line, it needs to be topped up. A low brake fluid level indicates a leak or worn brake pads. Overfilling past the MAX line can cause brake fluid spillage and damage paintwork. When checking, wipe off any dirt or debris from the reservoir cap before opening. Be sure to close it securely when finished.
Check the level with the vehicle on level ground, with the engine off. Visually inspect the fluid level through the translucent walls of the reservoir. Remove the cap only if the level is unclear. The level rises slightly as the brake pads wear down. If it is at or below the MIN line, top it up immediately and inspect the brakes for leaks.
Checking Brake Fluid Color
The color of your brake fluid is a good indicator of its condition. Fresh, uncontaminated brake fluid should have a clear, light amber color. Over time and use, brake fluid can start to darken as it becomes contaminated with moisture, Copper, and other particles from the brake system.
You should visually inspect the color of your brake fluid regularly by locating the brake fluid reservoir under the hood and looking at the fluid through the translucent reservoir. Good, fresh brake fluid will look clear to light amber in color. If the brake fluid appears dark brown or black, that is a sign that it has become heavily contaminated and should be flushed and replaced immediately.
The color change happens slowly over time, so you may not notice it unless you make a point of periodically checking the reservoir. Dark, contaminated fluid will still allow the brakes to function for some time, but eventually the moisture and particles in the fluid will greatly reduce braking performance and lead to complete brake failure. Catching discolored brake fluid early and replacing it can help avoid this dangerous situation.
The takeaway is to check the color of your brake fluid regularly as part of routine maintenance. Clear to light amber fluid is good to go. Once it starts turning noticeably dark brown or black, it’s time to replace the contaminated brake fluid right away.
Checking Brake Fluid Clarity
Brake fluid should have a clear, transparent appearance without any cloudiness. Cloudy or opaque brake fluid is a sign that condensation or moisture has contaminated the fluid. This moisture reduces the boiling point of the brake fluid, which can lead to vapor lock in the brake system when the brakes get hot.
Moisture contamination happens over time as brake fluid is hygroscopic, meaning it absorbs moisture from the air. The small rubber seals in the brake system allow water vapor to seep in gradually.
To check the clarity, examine the color of the fluid in the reservoir or on the dipstick if your vehicle has one. The brake fluid should look completely clear and transparent. Any cloudy appearance indicates moisture contamination. The cloudier it looks, the more moisture has entered the system.
If you notice cloudy or contaminated brake fluid, have it flushed and replaced immediately by a professional technician. Driving with moisture-contaminated brake fluid is unsafe and can lead to brake failure.
Checking Brake Fluid Smell
Fresh, uncontaminated brake fluid should have no discernible odor. Brake fluid is formulated to be odorless and any odor likely indicates contamination from external sources.
The most common odor in contaminated brake fluid is a sweet, syrupy smell. This distinct sweet odor is caused by brake fluid absorbing moisture from the air. As brake fluid absorbs moisture, its boiling point is lowered. The reduced boiling point allows the moisture to vaporize under high brake system temperatures, causing a compression of the brake fluid which leads to a loss of braking power. The sweet smell serves as an indicator that moisture contamination has occurred.
If you detect a sweet smell when checking your brake fluid, it means moisture has contaminated the fluid and degraded its performance. The fluid should be flushed and replaced as soon as possible to avoid dangerous brake failure.
Other odors may also indicate problems with the brake fluid or brake system components. For example, an oily smell can mean the brake fluid has absorbed mineral oil from deteriorating brake hoses or wheel cylinders. A burnt odor usually means overheated brake fluid from excessive braking. In either case, the brake fluid should be replaced if any unintended odors are noticed.
Remember, fresh brake fluid should always be odorless. Any odor upon inspection means moisture or other contaminants have degraded the fluid. If you notice a sweet, oily, burnt, or otherwise unusual smell, have a mechanic flush and replace the brake fluid before driving the vehicle again.
When to Change Brake Fluid
Brake fluid should be changed according to your vehicle manufacturer’s recommended maintenance schedule. For most vehicles, brake fluid changes are required every 2-3 years or 24,000-36,000 miles.
However, brake fluid may need to be changed more frequently in certain conditions. Signs that your brake fluid needs to be flushed and replaced include:
- Brake fluid appears dark, cloudy or contaminated
- Brake pedal feels soft or spongy
- Braking distances seem longer
- ABS or brake fluid warning lights come on
- Evidence of leaks or damage in the brake system
Moisture buildup over time through microscopic pores in hoses and internal rubber seals is the primary cause of brake fluid contamination and the need for fluid replacement. Heat from braking also causes brake fluid to break down. Replacing dirty, old brake fluid can restore braking performance and prevent complete brake failure.
Dangers of Contaminated Brake Fluid
Contaminated brake fluid poses serious dangers and should not be ignored. As brake fluid becomes old and contaminated, its effectiveness decreases significantly.
The most concerning danger is decreased braking ability. Brake fluid works by transferring mechanical brake pedal pressure into hydraulic pressure in the brake lines. Contaminated fluid will not transfer pressure as effectively, resulting in poor braking power.
In extreme cases, badly contaminated brake fluid can cause complete brake failure. The brakes may feel soft or spongy before ultimately losing the ability to stop the vehicle entirely. This poses an extreme safety risk.
In addition to reduced braking power, contaminated brake fluid allows corrosion and deposits to build up in the brake lines and calipers. This can lead to expensive damage over time.
Replacing dirty brake fluid regularly is crucial to avoid danger. Any signs of discoloration, cloudiness or particles mean the fluid should be flushed and replaced immediately.
DIY Brake Fluid Change
Changing your brake fluid is something you can do yourself at home if you have some automotive experience and the right tools. Here are the steps for a DIY brake fluid change:
Tools and Supplies Needed
- Jack and jack stands
- Wrench set
- Funnel
- Brake fluid (DOT 3 or DOT 4)
- Rags
- Drip pan
- Clear hose or tubing
Step-by-Step Instructions
- Lift up the vehicle using the jack and secure it on jack stands.
- Locate the brake fluid reservoir under the hood. Remove the cap and top off the reservoir with fresh brake fluid.
- Starting with the wheel furthest from the reservoir, remove the brake caliper bleeder valve cap.
- Attach one end of the clear hose to the bleeder valve, and submerge the other end in a container with some fresh brake fluid.
- Slowly open the bleeder valve and let the old brake fluid drain into the container.
- Once the fluid runs clear, close the bleeder valve. Refill the reservoir as needed.
- Repeat steps 3-6 for each wheel caliper. Always work from furthest to closest to the reservoir.
- Top off the brake fluid reservoir and replace the cap.
- Test brakes before driving.
Be sure to dispose of the old brake fluid properly. And remember to monitor your brake fluid level and condition on a regular basis.
Professional Brake Fluid Change
Getting a professional brake fluid change at a repair shop is recommended if you don’t feel comfortable doing it yourself. The average cost for a brake fluid flush at a shop is between $80-$150. The exact price can vary depending on the make and model of your vehicle and your location.
There are a few times when it’s best to have a professional mechanic perform the brake fluid flush instead of doing it yourself:
- If your vehicle has an antilock braking system (ABS) – the ABS module needs to be cycled during the process which requires special tools
- If you don’t have access to jack stands and tools needed to access the brake master cylinder reservoir
- If you’ve never performed this maintenance before and aren’t confident in your abilities
- If your brake fluid is extremely contaminated and has not been flushed in a very long time
Repair shops have the expertise to properly bleed and flush the entire brake system to remove all old fluid. They also have the right tools and equipment to safely lift up your vehicle and access the brake components without issue. For peace of mind, having a mechanic flush your brake fluid is a good idea if you are unfamiliar with the process.