“Making a car stop is a fundamental requirement of a vehicle which requires a couple of integral components of which brake fluid is one them.”
What is brake fluid and what does it do?
Brake fluid is a type of hydraulic fluid used in vehicle brake and clutch systems.
When you press on the brake pedal, brake fluid helps transmit the force from the brake pedal to the brake pads or shoes, which in turn clamps against a brake rotor or drums, to help slow down your wheels until your vehicle stops.
Choosing the right brake fluid for your use-case.
With many different types of brake fluids in the market, its important to understand what you’re choosing so that you can make the best informed choice.
Fortunately for us, the Department of Transportation (DOT) and Society of Automotive Engineers (SAE) have defined a Standard to help maintain the performance of brake fluids in both low and high temperatures, as well as minimum boiling temperatures for manufacturers to adhere to. These Standards help guide us to choose the right type of brake fluid to use for our specific applications.
Whilst there are other brake fluid standards outside of the DOT standard, we’ll be focusing on the 3 most popular DOT ones. The table below helps us understand a bit more about the main categories:
Brake Fluid Rating | Boiling Point (Dry) | Boiling Point (Wet) | Benefits | Cons |
DOT 3 | Up to 205°C | Up to 140°C | Less rubber component expansion, better protection against corrosion |
Eg. Motul DOT 3&4 |
DOT 4 | Up to 230°C | Up to 155°C | Higher dry and wet boiling points, required for brake systems that produce more heat |
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DOT 5 | Up to 260°C | Up to 180°C | Silicone-based, does not absorb moisture, does not damage paint |
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Source: https://nubrakes.com/blog/brake-fluid/
Dry vs Wet
Brake fluid is hygroscopic in nature and absorbs moisture from the air. This moisture dilutes the brake fluid, which then lowers its effectiveness and is the primary reason why it needs to be changed frequently.
The Dry Boiling Point of brake fluid refers to the boiling temperature of fresh, new brake fluid from an unopened container where no moisture has been absorbed.
Whereas the Wet Boiling Point is defined as the temperature DOT brake fluid will begin to boil after it has absorbed 3.7% water by volume.
How often should I change my brake fluid on my passenger car?
DOT brake fluid will reach the defined Wet Boiling Point after roughly 2 years, which is why it is advisable for passenger cars to change your brake fluid every 1-2 years.
How often should I change my brake fluid, if I track my car?
The answer to this question draws parallels to our answer to how many track days can I safely do before changing my oil. We know that a car that hits the track deteriorates engine oil quicker compared to a car that only gets daily driven, and brake fluid in a car that sees track time is no different.
The environment that a brake fluid gets put under alters the way it reacts and behaves and the more heat and stress that brake fluid is put under, the quicker it loses its out-of-the-box properties including its ability to prevent corrosion, lubricate parts and ability to make a car stop.
Using an arbitrary number of months when considering motorsport use to define when you should change your brake fluid is anyone’s best guess. Scientifically, an oil analysis test (yes, this test also can be used for analysing brake fluid!) will give you the data and proof to tell you when your brake fluid has degraded enough for you to change it.
However pushing your brake fluid change interval to the extreme can be dicing with death. Get it wrong and your brake fluid will boil causing your brakes to fail, whilst you’re barrelling down the main straight at 200kmph.
So to avoid nasty situations like this, we recommend a conservative approach when it comes to brake fluid change intervals and to change it frequently enough that you don’t have to wonder should I change it now? This ensures you have the freshest possible fluid to guarantee your day won’t be ruined or cut short by fading brakes.

Photos courtesy of Brett Swain and Gwyn Morgan @ GSS.
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