If you’ve ever found yourself with a hydraulic jack that needs fluid but only have brake fluid nearby, you’re not alone. It’s a common question among DIYers and even professional mechanics—can you use brake fluid in a hydraulic jack?
Let’s clear the air: technically you can, but you absolutely shouldn’t. While both brake fluid and hydraulic jack oil may seem similar because they’re both hydraulic fluids, they are engineered for very different purposes. Using brake fluid in a hydraulic jack can damage the seals, reduce performance, and eventually destroy the jack.
In this blog, I’ll walk you through the differences, potential consequences, alternatives, and what to do if you’ve already poured the wrong fluid in. Let’s think from the real user perspective—you’re busy, you’re trying to get a job done, and you just want clear answers.
Why You Might Consider Using Brake Fluid in a Jack
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You’re in the middle of a project and don’t have hydraulic jack oil
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You assume all hydraulic fluids are interchangeable
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You read something online suggesting it’s okay
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You’re trying to save money or time
While these are understandable reasons, they lead to a critical misunderstanding of fluid chemistry and mechanics.
The Key Differences: Brake Fluid vs. Hydraulic Jack Oil
Here’s a simple comparison:
| Особенность | Тормозная жидкость | Hydraulic Jack Oil |
|---|---|---|
| Base Composition | Glycol-ether based (mostly synthetic) | Mineral oil based |
| Additives | Anti-corrosion, anti-boil, water-absorbing | Anti-foam, seal protectants |
| Viscosity (thickness) | Low to moderate | Thicker and more stable |
| Water Absorption | Hygroscopic (absorbs water) | Non-hygroscopic (resists water) |
| Compatibility with Seals | Can damage rubber seals in jacks | Safe for jack seals |
| Typical Use | Braking systems in vehicles | Jacks, hoists, lifts |
Why Brake Fluid Is Dangerous for Jacks
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Seal Damage
Most hydraulic jacks use seals made for mineral oils. Brake fluid, especially DOT 3 or DOT 4, is highly corrosive to these rubber materials, causing swelling, softening, or cracking. -
Water Absorption (Hygroscopic Nature)
Brake fluid absorbs moisture from the air. Over time, this water can corrode internal jack components and reduce lifting power. -
Chemical Breakdown
Brake fluid breaks down differently under pressure and heat. It can foam, oxidize, or gum up your jack’s internal passages. -
Reduced Efficiency
You’ll likely notice slower lift speed, jerky operation, or even complete jack failure over time.
What If I Already Used Brake Fluid in My Jack?
Don’t panic—but don’t ignore it either.
Step-by-Step Recovery:
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Stop using the jack immediately.
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Drain all the brake fluid from the jack reservoir.
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Flush the system with mineral spirits or a proper flushing fluid (not water).
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Let it dry completely.
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Refill with proper hydraulic jack oil.
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Test cautiously for leaks, noises, or poor operation.
If your jack starts leaking or becomes inconsistent, the seals may already be damaged. In that case, consider a full rebuild or replacement.
What Should I Use Instead?
Use only hydraulic jack oil or ISO 32/46 hydraulic fluid, depending on your jack’s manual. Here’s a list of acceptable alternatives:
| Recommended Fluids | Примечания |
|---|---|
| Hydraulic Jack Oil (ISO 32) | Best option, widely available |
| ISO 32 Hydraulic Oil | Light viscosity, good cold weather use |
| ISO 46 Hydraulic Oil | Slightly thicker, better for heavy duty |
| AW-32/46 Oil | Includes anti-wear additives |
| Automatic Transmission Fluid (ATF)* | Emergency use only; not ideal long-term |
*ATF is sometimes used in an emergency, but may foam or affect seal performance over time.
Часто задаваемые вопросы
Q: Why is brake fluid bad for my hydraulic jack?
А: It breaks down rubber seals, absorbs water, and doesn’t maintain proper viscosity under pressure.
Q: Can I mix brake fluid and jack oil?
А: Нет. Mixing can cause chemical reactions, damage seals, and reduce performance.
Q: Is it ever okay to use brake fluid temporarily?
А: Not recommended. Even short-term use can start damaging seals.
Q: How can I tell if my jack is damaged from brake fluid?
А: Look for leaks, hissing sounds, jerky movement, or failure to lift.
Q: What if I only used a small amount of brake fluid?
А: Even a small amount can start seal degradation. Flush it out ASAP.
Final Thoughts
Using brake fluid in a hydraulic jack might seem like a shortcut, but it’s one that leads to long-term problems. Your best bet is to stick to jack-specific oil and avoid improvisation unless it’s a true emergency—and even then, only with careful follow-up.
If you’ve made the mistake already, don’t beat yourself up. Just flush it out and move forward the right way. When it comes to tools that lift thousands of pounds, it’s always best to play it safe.
