Brake fluid has specific indicators that warn you the fluid is no longer suitable. One is its minimum boiling point, which reduces with age; the other is its color. In this article, we are going to answer a few questions that get raised:
- Why does brake fluid change color?
- What color brake fluid is bad?
- What should you do if the brake fluid changes color?
What Color Is Good Brake Fluid?
Brake fluid is available in different colors, but each color represents a separate “DOT” rating and the chemicals used to make the fluid. DOT stands for Department Of Transport, which sets each fluid grade’s minimum boiling point requirement.
- DOT 3, 4 & 5.1 – All three brake fluids used in standard road vehicles are clear with a yellow tint in color; some brands supply a darker yellow liquid than others. It should be a very similar color and consistency to olive oil. The minimum required boiling point on DOT 3 fluid (the lowest) is 205 degrees Celcius (401 degrees Fahrenheit). You can read more about brake fluid boiling points in this article.
- DOT 5 – Dot 5 brake fluid Comes in a few different colors but is mainly a mix between pink and red; however, you may also find it in purple. Because DOT 5 is silicone-based, it does not absorb water and has the highest boiling point. It is usually only found on race cars and military vehicles where high boiling points are critical.
- LHM – LHM is a bright, green fluid, usually only found on cars with self-leveling suspension systems. Citroens are the most popular vehicles that use this fluid.
What Color Is Bad Brake Fluid?
The standard DOT 3, 4 & 5.1 brake fluids turn dark brown or black when bad. They will have a similar color to dirty engine oil. There are other ways to check if the brake fluid is unsuitable, such as checking the fluid against its minimum boiling point using a brake fluid tester. Most mechanics will start their brake fluid inspection by checking its color first.
Because both LHM and DOT5 are completely different fluids that operate differently, it is tough to determine whether these fluids are bad by color. LHM is already green and can become a darker green fluid when bad. Checking the boiling point of LHM is the best way to determine if it needs replacing yet.
Because DOT5 is mainly found in race cars, the brakes must be in a new condition before each race, so the brake fluid will often be replaced. DOT5 brake fluid is tricky to determine its condition by color. The color is less crucial than the boiling point in its application.
What Causes Brake Fluid to Change Color?
Brake fluid turns dark for several reasons. The leading cause is moisture absorption with age because most brake fluids are hygroscopic; moisture gets absorbed through rubber brake hoses. Brake fluid also absorbs dirt and contaminants in the brake system from rubber hoses, brake seals, and deteriorating metal components, all of which affect the fluid’s color.
The moisture it absorbs will cause the brake fluid to take on its darker color and lower its wet boiling point. One thing to consider is that if you live in a humid climate, you can expect the brake fluid to absorb moisture quickly.
If the brake fluids’ boiling point drops below the minimum, brake fade can occur under heavy braking. Because the brake fluid boils at a lower temperature, it overheats and will no longer function correctly. This can result in a spongy brake pedal when driving.
What Should You Do if the Brake Fluid Is Changing Color?
Having your mechanic inspect the brake fluid is the best option; they will be able to confirm the fluid needs replacing. However, if you open the brake fluid reservoir cap to find dirty brake fluid, the best option is to flush and replace the brake fluid completely.
A brake fluid flush is usually carried out with a brake pressure bleeder to aid in quickly removing and replacing brake fluid. A brake fluid change can be carried out in as little as 30 minutes with prior experience and the correct tools, so it’s usually a cheap maintenance task.
It is possible to replace the brake fluid at home with the help of another. One person must pump and press the brake pedal while you open and close the bleed nipple. However, you still require a brake bleed bottle because brake fluid is corrosive; if it leaks onto the floor, it will lift the paint off a workshop floor or stain a driveway.
How Often Should You Change the Brake Fluid?
You should replace the brake fluid every 24 months. It is often carried out on most vehicles as part of a service schedule. However, you should check your service schedule or consult the car manufacturer to confirm. Brake fluid replacement isn’t an item that is recommended based on specific mileage because usage does not determine how quickly the brake fluid degrades. Only the brake fluid age, boiling point, and potentially the climate do.
Frequently Asked Questions
What Causes Brake Fluid To Discolour?
Moisture absorption alongside heat causes brake fluid to change color. Moisture gets absorbed with age, this lowers the brake fluid boiling point. When the brake fluid boils, the fluid discolors.
Is It Bad To Drive With Dirty Brake Fluid?
It is not safe to drive with dirty brake fluid. Dirty brake fluid is a sign the boiling point is low. Driving with dirty brake fluid could put you in a dangerous situation if the brake fluid gets hot enough to boil. When this happens you will not be able to stop car as quickly.
Final Remarks
To summarise, why does brake fluid change color? It changes color because of the contaminants, and moisture absorbs into the fluid. If you find the brake fluid in your vehicle is dark brown or black, you should replace this fluid as soon as possible. Dirty brake fluid that has absorbed moisture will have a lower boiling point, which means the brakes may not work correctly.
