# Brake Fluid Info
> Brake fluid isn't fancy, but it's the lifeblood of your braking system. Knowing how it works and how to maintain it can help put a stop to bad brakes!
Source: https://help.flyinmiata.com/en_us/brake-fluid-info-ByEwRM89ex
Last updated: 2026-02-06T23:43:04.098Z
Brake fluid doesn’t usually get much attention, but it’s the lifeblood of your braking system. Knowing what it does, how it works, and how to maintain it can make the difference between a car that stops confidently and one that puts you at risk.
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## Key Properties of Brake Fluid
### **Boiling Point:**
* Brake fluid must withstand the extreme heat generated during braking.
* Brake fluid is a non-compressible hydraulic fluid. When it reaches its boiling point, it turns into a compressible gas, which can cause a spongy or unresponsive brake pedal.
### **Hygroscopic Nature:**
* Brake fluid absorbs moisture from the air over time.
* Benefits: Helps prevent rust inside the brake system and reduces the risk of freezing.
* Drawback: Water content lowers the boiling point, making brakes more likely to fade under heat.
### **Dry vs. Wet Boiling Points:**
* Dry boiling point: Fresh brake fluid with no water absorbed.
* Wet boiling point: Brake fluid after it has absorbed some moisture, which is the real-world condition most drivers face.
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## Brake Fluid Specifications (DOT Ratings)
Brake fluids are classified by the U.S. Department of Transportation (DOT) based on their boiling points and chemical makeup:
* **DOT 3**: Glycol-based, common for older or economy vehicles; lower boiling point.
* **DOT 4**: Glycol-based, widely used in modern cars; higher boiling point than DOT 3.
* **DOT 5**: Silicone-based, not hygroscopic; incompatible with most ABS systems.
* **DOT 5.1**: Similar boiling point to DOT 5 but glycol-based, so it works with systems designed for DOT 3/4.
We typically prefer DOT 4 for both street and track-driven Miatas. It generally has higher dry and wet boiling points while still being compatible with DOT 3 fluid (so you can use DOT 4 brake fluid to top off a brake system that is currently filled with DOT 3).
_**\*Not all brake fluid is made equal:**_ Brake fluid produced by one manufacturer may have different dry and wet boiling points than another brake fluid of the same specification, but produced by a different manufacturer. It's always best to check the spec sheets when comparing different brands of brake fluid if you're looking for the highest-rated boiling points.
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## Maintenance: How Often Should You Change Brake Fluid?
* **Street Cars:** Once per year is recommended to maintain performance and safety. As fluid gets older, it absorbs water and becomes more prone to boiling.
* **Track Cars / High-Performance Use:** Change more frequently, as fluid degrades faster under extreme heat and stress.
Fresh brake fluid is usually clear to light amber and somewhat translucent. As it ages, it turns dark brown or nearly black and opaque, a sign that it has absorbed moisture and contaminants and is due for replacement. Can't remember the last time it was changed? Your brakes will never complain of getting fresh fluid.
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## Bleeding Brakes: Removing Air and Old Fluid
Bleeding brakes ensures no air bubbles remain in the system and that fresh fluid reaches the calipers. Common methods include:
* **Pump and Hold**: One person pumps the brake pedal a few times, then holds constant pressure on the pedal while another opens/closes the bleeder valve.
* [**Speed bleeders:**](https://flyinmiata.com/products/speed-bleeders?_pos=1&_sid=eebb29515&_ss=r) A standard bleeder screw with an internal check valve. It will let fluid and air escape, but won't let any air back into the system.
* **Brake bleeder/vacuum pump:** A tool that creates a vacuum or pressure in the brake lines.
It's important to start with the caliper **furthest from the master cylinder** and work your way closer. For Miata-specific instructions, check out our full guide: [How to properly and effectively bleed a brake system.](https://help.flyinmiata.com/articles/-H1t9Z1kfa)
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In short, brake fluid must resist boiling, transmit pedal force reliably, and be replaced regularly since it naturally absorbs moisture. Choosing the right DOT fluid for your vehicle, keeping up with fluid changes, and bleeding the brakes correctly will ensure your car stops safely and consistently, whether you’re on the street or the track.
Need a visual aid from our favorite Canadian Miata Guru? Keith Tanner covered this same topic in a YouTube video: [Brake Fluid Tech (FM Live)](https://www.youtube.com/watch?v=7-IsZHyEQvE&list=PLqtVay6fh_4yrSzgp1mUQxm_kDAsVttp-)