DOT 5 To DOT 4: A Step-by-Step Tutorial

Posted on: Mar 31, 2025 | Reading Time: 4 min read

DOT 5 to DOT 4: A Step-by-Step Tutorial – Can You Do It?

Switching brake fluids, especially from DOT 5 to DOT 4, isn't a simple fluid change. It requires meticulous attention to detail because these fluids are fundamentally incompatible. This comprehensive guide will walk you through the process, highlighting critical safety precautions and explaining why a direct swap is strongly discouraged.

Why You Shouldn't Simply Swap DOT 5 and DOT 4

Before diving into the procedure, it's crucial to understand why mixing DOT 5 and DOT 4 is dangerous. DOT 5 is silicone-based, while DOT 4 is glycol-ether based. These fluids are chemically incompatible; mixing them can lead to:

Fluid Degradation: The chemical reaction between DOT 5 and DOT 4 can compromise the performance of both fluids, potentially reducing their braking effectiveness.
System Damage: The reaction can also create sludge or precipitates within the braking system, clogging lines and damaging components like calipers, master cylinders, and ABS modules. This can lead to costly repairs or even catastrophic brake failure.
Voiding Warranty: Attempting this conversion likely voids any warranties related to your braking system.

Is Switching From DOT 5 to DOT 4 Possible?

The short answer is: Yes, but only with a complete system flush. This is not a simple task and should only be undertaken by experienced mechanics. A simple drain and refill won't suffice due to the incompatibility of the fluids. Residual DOT 5 will compromise the new DOT 4.

The Necessary Steps for Converting from DOT 5 to DOT 4

This process requires considerable mechanical skill and the right tools. If you lack the experience, it's strongly recommended to take your vehicle to a qualified mechanic.

1. Gather Your Supplies:

New DOT 4 brake fluid: Ensure you purchase enough fluid to completely flush the system.
Brake fluid flushing machine (recommended): This greatly simplifies the process, ensuring complete fluid removal.
Alternatively, a gravity bleed kit: If using this method, prepare for a more time-consuming process.
Wrenches: To access and remove brake bleed valves.
Clear tubing: To connect to the bleed valves.
Clean containers: To collect the old brake fluid.
Gloves: To protect your hands from the corrosive brake fluid.
Safety glasses: To protect your eyes from splashes.
Shop rags or paper towels: For cleanup.

2. Complete Brake System Flush:

This is the most critical step. The goal is to remove all traces of the DOT 5 brake fluid. Using a flushing machine is highly recommended. This machine circulates fresh DOT 4 brake fluid throughout the system, pushing out the old fluid. If you're using a gravity bleed kit, prepare for a lengthy process, requiring multiple bleed cycles at each caliper and wheel cylinder.

3. Bleed Each Brake Caliper/Wheel Cylinder:

Follow the bleeding procedure specific to your vehicle. This generally involves opening the bleed valve on each caliper/wheel cylinder while an assistant keeps the brake pedal depressed. This removes air and any remaining old fluid.

4. Verify Fluid Level:

After bleeding, check the brake fluid reservoir level and top off with fresh DOT 4 as needed. Avoid overfilling.

5. Test the Brakes:

Once the system is flushed and bled, test the brakes thoroughly in a safe, controlled environment. If the brakes feel spongy or ineffective, you may need to repeat the bleeding process or seek professional help.

Frequently Asked Questions (FAQs)

Can I mix DOT 3 and DOT 4 brake fluids?

Yes, DOT 3 and DOT 4 are compatible and can be mixed, but it's best practice to use only one type for optimal performance. If mixing, make sure to choose the highest quality fluid for your system.

What happens if I accidentally mix DOT 5 and DOT 4?

Accidental mixing of DOT 5 and DOT 4 can result in fluid degradation, sludge formation, and potential damage to the brake system. A complete system flush is required to mitigate risks.

How often should I change my brake fluid?

Brake fluid should be flushed and replaced every 2-3 years or according to your vehicle manufacturer's recommendations.

What are the differences between DOT 3, DOT 4, and DOT 5 brake fluids?

Each DOT rating represents a different fluid formulation with varying boiling points and properties. DOT 3 and 4 are glycol-ether based, while DOT 5 is silicone-based. Consult your vehicle's owner's manual for the correct type of brake fluid for your vehicle.

Disclaimer: This information is for educational purposes only. Brake system maintenance is complex and potentially dangerous. Always consult your vehicle's owner's manual and seek professional assistance if you are unsure about any aspect of this process. Improper brake maintenance can lead to serious injury or death.