If you’ve ever attempted a DIY brake job, one question that’s bound to come up is: Should I open the brake fluid reservoir when bleeding the brakes? This is a simple question with important consequences, especially when your safety—and your vehicle’s braking performance—are on the line.
In questo articolo, I’ll walk you through everything you need to know about this topic. Whether you’re a beginner doing your first brake job or someone looking to confirm what you’ve heard online, this guide answers all your questions clearly and thoroughly.
The Quick Answer: SÌ, Open the Brake Fluid Reservoir When Bleeding Brakes
When bleeding brakes, you should open the brake fluid reservoir cap. This allows air to escape and ensures the master cylinder can draw in fluid properly as you remove air bubbles from the brake lines.
Why Opening the Reservoir Matters
Let’s break it down from a user’s point of view—someone who just wants their brakes to work reliably.
| Reason | Explanation |
|---|---|
| Air Escape | With the cap off, air trapped in the system can move freely, reducing the chance of pressure buildup. |
| Fluid Replenishment | As brake fluid leaves the reservoir and travels through the lines, the open cap allows air to enter the top of the reservoir so that more fluid can flow out. |
| Avoiding Vacuum Lock | A closed cap can create a vacuum that restricts fluid movement, making bleeding inefficient or even impossible. |
| Monitoring Fluid Level | You can easily keep an eye on the fluid level and top it up before it drops too low (which would let more air in). |
How to Safely Open the Reservoir During Bleeding
When opening the reservoir, follow these precautions:
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Clean the cap and surrounding area first. Brake fluid is extremely sensitive to contamination. Dirt or debris falling into the fluid can cause long-term damage to your brake system.
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Place a rag or towel around the reservoir. This protects paint and components from accidental drips. Brake fluid is corrosive to painted surfaces.
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Open the cap gently. It may be pressurized slightly. Remove the diaphragm or rubber gasket carefully and place it in a clean area.
Step-by-Step Guide: Bleeding Brakes with an Open Reservoir
Here’s a simplified overview that you can follow:
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Park your car on a level surface and secure it with wheel chocks.
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Remove all wheels for better access to the bleeder screws (optional but recommended).
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Open the reservoir cap and check that the fluid is at the proper level.
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Attach clear tubing to the bleeder screw and place the other end into a container partially filled with clean brake fluid.
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Have a helper press the brake pedal slowly while you open the bleeder screw.
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Watch for air bubbles and close the screw when only fluid flows out.
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Top off the reservoir after every few pumps to avoid running dry.
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Repeat for each wheel, usually in this order: RR > LR > RF > LF (furthest to closest to the master cylinder).
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Re-tighten all bleeder screws, recheck the fluid level, and reinstall the reservoir cap.
Common Mistakes to Avoid
| Mistake | Why It’s a Problem |
|---|---|
| Bleeding with cap closed | Can cause inconsistent flow or poor results due to pressure imbalance. |
| Letting the reservoir run dry | Introduces new air into the system, undoing your progress. |
| Not topping off fluid frequently | You must maintain fluid level throughout the process. |
| Over-tightening bleeder screws | Can strip threads or break them, leading to costly repairs. |
What If You Forget to Open the Reservoir?
If you’ve already started bleeding without opening the reservoir, stop and open it now. The process won’t work properly unless air can move freely through the system. You may have to restart the bleeding from the beginning to ensure all air is removed.
Can I Leave the Cap Off Completely?
You can leave the cap loose or resting on top—you don’t need to remove it completely. This minimizes contamination risk while still allowing airflow.
PUNTO 3 vs DOT 4 vs DOT 5 Brake Fluids
Since you’re working with the reservoir, it’s worth knowing your brake fluid type. Never mix incompatible types.
| Brake Fluid Type | Boiling Point (Dry/Wet) | Mix Compatibility |
|---|---|---|
| PUNTO 3 | 401° f / 284° f | Compatible with DOT 4 |
| PUNTO 4 | 446° f / 311° f | Compatible with DOT 3 |
| PUNTO 5 | 500° f / 356° f | Not compatible with DOT 3 O 4 (silicone-based) |
FAQ
Q: Can I bleed brakes alone?
SÌ, with tools like a vacuum pump or a one-man bleeder bottle, it’s possible to do it solo.
Q: How often should I bleed my brakes?
Typically every 2-3 years or whenever the pedal feels spongy or you’ve opened the hydraulic system.
Q: What if brake fluid overflows from the reservoir?
Wipe it immediately. Brake fluid can damage paint and plastic surfaces.
Q: Is it bad to get air into the reservoir?
Air entering the top of the reservoir is fine. You just don’t want it going down the brake lines. Keep the fluid level above the minimum line at all times.
Q: Should the car be on or off while bleeding?
The car should be off. You don’t want power assist interfering with fluid pressure.
Final Thoughts
Opening the brake fluid reservoir while bleeding the brakes is not just a good practice—it’s essential. It keeps the fluid flowing smoothly, prevents new air from entering the system, and makes the process more efficient and effective. Just be careful to avoid contamination and always keep an eye on the fluid level.
Whether you’re a DIYer or just trying to save a few bucks at the garage, understanding this simple step can make a world of difference in your braking safety.
