The list of fluids our vehicles require is a long one. Our vehicles rely on a variety of fluids to operate, and they all serve a very particular purpose. Brake fluid and power steering fluid are both hydraulic liquids, which leads me to wonder…
Can brake fluid be used for power steering? The answer is a resounding no. If you used brake fluid in your power steering system, it would cause significant damage.
Brake Fluid Vs Power Steering Fluid
Brake fluid and power steering fluid are both liquids used in a hydraulic system in modern vehicles, but the similarities don’t go much farther than that.
Brake fluid and power steering fluid were designed and refined over the years to serve very different purposes within vehicles, and they are not interchangeable.
In fact, putting brake fluid in your power steering reservoir will do more than just cause your power steering to lose efficiency. It will actually cause serious damage.
Here is an overview of the differences between brake fluid and power steering fluid.
| Brake Fluid | Power Steering Fluid |
| Composition: 60%-90% solvent, 5%-30% lubricant, 2%-5% additives | Composition: 85%-90% lubricant, 10%-15% additives |
| Usually Glycol-Ether based | Usually Petroleum-based |
| The main purpose is to transfer force into pressure in the brake system. | The main purpose is to lubricate the power steering pump. |
| The secondary purpose is to keep brake lines from corroding. | The secondary purpose is to provide pressure to the power steering system. |
| Caustic, will strip paint from your car | Not caustic |
| Light yellow in color when new. Amber to brown as it ages. | Yellow, amber or pink in color when new. Brown to black when it ages. |
| Low compressibility | Low compressibility, but not as low as brake fluid |
| Not a good lubricant | A good lubricant |
Not all properties of brake fluid will cause problems in your power steering. The two main reasons you can not use brake fluid in your power steering system are that brake fluid is caustic and that brake fluid has weak lubricating abilities.
Not Enough Lubricant in Brake Fluid
At only 5% to 30% lubricant, brake fluid would not work well as a lubricant for the power steering pump. It might offer some lubricant to the power steering pump, but not enough. The power steering pump requires the 85%-90% lubricant in power steering fluid.
Without proper lubricant, the moving pieces of the power steering system will not be able to move with the same ease. This is especially true for the places in the power steering system where metal moves against metal.
The result is that your power steering will falter and eventually fail.
Brake Fluid is Caustic
Considering brake fluid can strip the paint off your car, you can only imagine what it might do to a system that was not created to withstand its causticity.
Brake fluid would cause irreparable damage to the seals, gaskets, and rubber hoses in the power steering system. It will either cause them to swell and leak or cause parts of them to dissolve completely.
The power steering would fail completely.
Cost of Fixing the Problems Caused by Brake Fluid in the Power Steering
So what will all this cost you?
It depends on how much damage the brake fluid did, which would depend on how much brake fluid you poured in and whether it entered the entire power steering system.
Here are some ballpark numbers to help give you an idea. These are all estimates and can vary depending on your vehicle, location, and the mechanic you bring it to.
If you put brake fluid in your power steering, then you will need to flush out the bad fluid and replace it with new. If you cannot DIY it, then the cost will be $69.99 at the least (Source). The cost will vary depending on how much the power steering fluid your specific vehicle takes.
In order to repair the power steering system’s rack seals, the mechanic must dismantle the system. This will increase the labor costs of the job. For parts and labor, it can cost between $600 and $1,000 (Source).
The average cost to replace a hose in your power steering system including parts and labor is between $388 and $512 (Source).
If the lack of lubrication causes a problem with the pump itself, the average cost to replace it is between $459 and $659 (Source).
Where Does This Misconception Come From?
Perhaps you’ve heard from a friend or family member or someone else you trust that brake fluid and power steering fluid are interchangeable. It seems to be a fairly common misconception.
I believe the root of this problem is that automatic transmission fluid was used in early power steering systems before power steering fluid existed.
This was possible because they are both primarily used as lubricants. The main difference between them is that automatic transmission fluid has more detergents.
Brake fluid seems to have got lumped into it, but brake fluid has never been used as power steering fluid.
What If You Put Brake Fluid in Your Power Steering System?
Brake fluid will cause damage to the power steering system. If you accidentally put brake fluid into your power steering system, you need to flush the system thoroughly. This video details the process, but I have also written it out.
Only try to flush your power steering system if you feel comfortable working on your own car, and you are ready for a bit of a mess.
- Do not drive the car or even turn it on. This will help keep the brake fluid from entering the power steering system, which will limit the damage it could cause. If you have not turned the car on, the brake fluid you poured should still be sitting in the reservoir.
- Open the power steering fluid reservoir and use a turkey baster to draw out as much fluid as you can. Have a container for the old fluid handy.
- If you aren’t comfortable working on your own car, you might want to find someone who is knowledgeable about vehicles to help you with the following steps.
- Jack up the car so the front wheels are off the ground and turn the steering wheel so that the front wheels move from back and forth. More fluid will appear in the reservoir.
- Use the turkey baster to get the rest of the fluid out of the reservoir.
- Now you will have to disconnect the low-pressure line and allow it to drain into a container.
- Turn the wheels back and forth to flush our more old fluid.
- Pour fresh power steering fluid into the reservoir and allow it to drain through the system and out into a bottle.
- Do this 3 times.
- Put everything back together and fill up your power steering system with power steering fluid.
- If you want to be extra careful, you can have the power steering system flushed again by a mechanic.
If you have already driven the car with brake fluid in the power steering, then you should get it to a mechanic to be flushed and to have any damage fixed.
Can Power Steering Fluid Be Used for the Brakes?
So, we know that brake fluid cannot be used for power steering, but can you use power steering fluid to top off your brake fluid?
The answer, as you might suspect, is no.
The rubber in brake lines is not designed to hold petroleum-based fluids like power steering fluid. The seals will begin to swell immediately upon contact with the steering fluid causing blockages in the brake line.
Even one pump of the brake pedal is enough to send the contaminated fluid through the entire brake system. The brake system will fail quickly after the power steering fluid is introduced.
The only fix would be to dismantle the brake system, clean out the lines, and replace any of the rubber pieces.
