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Fast ShippingBrake fluid is one of the most critical, yet often overlooked, components of your car’s safety system. Understanding what it is, how it works, and when to change it helps ensure reliable braking performance.
What is brake fluid?
Brake fluid is a hydraulic liquid that transfers the pressure from your foot on the brake pedal to the calipers and wheel cylinders. Without it, your brakes would not generate the stopping power you rely on every day. A good fluid must remain stable under high heat, resist boiling, and protect the brake system against corrosion.
Different types of brake fluid
Brake fluids are classified by the U.S. Department of Transportation (DOT) standards. Here are the most common types:
- DOT 3: Glycol-based, common in older vehicles and light-duty cars.
- DOT 4: Glycol-based with higher boiling points, standard in most modern vehicles.
- DOT 4 LV (Low Viscosity): Designed for modern ABS and stability systems in colder climates.
- DOT 5: Silicone-based, used in certain classic or military vehicles. Not compatible with DOT 3, 4, or 5.1.
- DOT 5.1: Glycol-based, with very high boiling points, often used in performance or heavy-duty applications.
Tip: Always check your vehicle’s cap or manual before choosing fluid. Mixing incompatible types can damage your system.
How to know when it’s time to change
- Brake pedal feels soft or spongy after repeated stops.
- Fluid looks dark brown instead of clear or light amber.
- Warning lights or ABS faults linked to hydraulic pressure.
- Testers show moisture contamination above 3%.
- The recommended service interval has been reached.
How often should brake fluid be changed?
Most manufacturers recommend replacing brake fluid every 2 years or roughly 24,000 to 40,000 km. If you drive in harsh conditions, tow heavy loads, or participate in track events, you may need to replace it more frequently.
Step-by-step instructions for changing brake fluid
- Park the car on a level surface and secure it safely.
- Remove the old fluid from the reservoir with a syringe or baster.
- Refill the reservoir with the recommended fresh brake fluid.
- Bleed the brakes at each wheel in the proper order (usually farthest to closest from the master cylinder).
- Keep topping up the reservoir during bleeding to avoid introducing air.
- Once fresh, clear fluid comes out at each wheel, close the bleeders and check pedal feel.
Driving after a brake fluid change
After the service, test the pedal while stationary—it should feel firm. On your first drive, brake gently in a safe area to ensure the system feels normal. Avoid aggressive braking until you’re confident the job is done correctly.
Frequently Asked Questions
Can I use DOT 5 instead of DOT 4?
No. DOT 5 is silicone-based and not compatible with glycol fluids like DOT 3, 4, or 5.1.
Is it okay to mix DOT 4 and DOT 5.1?
Yes. Both are glycol-based and compatible, but always use the type recommended by your vehicle manufacturer.
Why is brake fluid dark?
Heat and moisture contamination break down the fluid and cause it to darken. Dark fluid is a clear sign it should be changed.
Can I change it myself?
Yes, with the proper tools and care. However, if your vehicle has complex ABS systems, it’s safer to have a professional do the work.