Are Brake Fluid and Power Steering Fluid the Same?

[OLincoln]

Brake fluid and power steering fluid are not the same. Brake fluid, also known as hydraulic brake fluid, is the liquid medium that transmits braking pressure in a vehicle's hydraulic braking system. Power steering fluid, also referred to as steering fluid or steering oil, is the hydraulic oil used in the steering system to transmit hydraulic pressure. Brake fluid has characteristics such as good viscosity-temperature performance, low water absorption, excellent low-temperature fluidity, oxidation resistance, rubber compatibility, low freezing point, high boiling point, and resistance to vapor lock at high temperatures. It undergoes minimal quality changes during vehicle use and does not cause corrosion to metal or rubber components. In contrast, power steering fluid has higher viscosity, poor fluidity, a distinct odor, and some corrosive properties.

[DelJulian]

I've been fixing cars for over a decade, and these two fluids are definitely not the same thing. Brake fluid is specifically for hydraulic brake systems and must withstand high temperatures and pressure, otherwise the brakes will feel spongy and that's extremely dangerous. Common grades like DOT3 and DOT4 feel slippery on your hands and can even burn your skin. As for power steering fluid? That's what makes turning the steering wheel smooth and easy, usually red or yellow in color, with a viscosity more like regular engine oil. The worst part is mixing them up—I've seen people take shortcuts and add the wrong fluid, resulting in swollen rubber brake components that leaked and nearly caused a major accident when the steering wheel suddenly locked up. Their replacement intervals also differ significantly: brake fluid needs its moisture content tested every two years, while power steering fluid doesn't require frequent checks unless the steering wheel starts making creaking noises.

[JosiahFitz]

When I first started driving, I couldn't tell the difference either, so I specifically asked the mechanic during maintenance. The brake fluid is crucial for the life-saving braking system. If you open the hood, you can see the brake fluid reservoir labeled with letters like DOT4. It's very fluid, almost like water. The power steering fluid is exclusively for the steering system, usually stored in a white reservoir with a steering wheel symbol, and its texture is more like salad oil. Once, a friend mistakenly added power steering fluid as windshield washer fluid, and the wiper blades were completely ruined. I recommend keeping an eye on these during maintenance, especially for older cars where rubber hoses may have deteriorated—leaks of these two fluids can corrode different components. I remember the last time my car was low on power steering fluid; turning the wheel felt as heavy as moving bricks, which is completely different from the sensation of brake failure.

[LaReid]

Look at the ingredients for the most straightforward understanding: Brake fluid is primarily composed of polyethylene glycol ether, which has particularly strong water absorption. Therefore, it must be replaced every two years; otherwise, the increased water content lowers the boiling point, and continuous braking may lead to vapor lock failure. Power steering fluid, on the other hand, is mostly formulated with mineral or synthetic oil, with a focus on oxidation resistance. Last time I tested data for both fluids: brake fluid should be replaced when water content exceeds 3%, as the boiling point can plummet from 265°C to 140°C; power steering fluid can continue to be used as long as its color doesn't turn black. The equipment for changing these fluids also differs. At a repair shop, replacing brake fluid requires two people to cooperate in pumping the brakes to bleed the air, while power steering fluid simply involves draining the old fluid and filling in the new one.

[LukeLee]

Here are two handy tips to tell them apart: First, smell them—brake fluid has a pungent alcohol-like odor, while power steering fluid is almost odorless. Second, test water absorption—place a drop on glass. Brake fluid turns cloudy by absorbing moisture within half an hour, whereas power steering fluid remains clear. My car suffered once when the brake fluid reservoir cap wasn't tightened properly. After the rainy season, the brake pedal suddenly sank halfway—I rushed to get it fixed in panic. My friend went further—she topped up her power steering fluid with kitchen olive oil, resulting in a noisy steering pump and an 800-yuan repair bill. Actually, the reservoir caps have icons: a circle with an exclamation mark for brake fluid, and a steering wheel symbol for power steering fluid.