Is Brake Fluid the Same as Power Steering Fluid?
4 Answers
Brake fluid and power steering fluid are not the same. Brake fluid, also known as hydraulic brake fluid, is a functional liquid in the vehicle's braking system that transmits pressure to enable the braking action on the wheel's braking system. Brake fluid does not undergo chemical reactions, is unaffected by high temperatures, and does not corrode, soften, or expand metal and rubber components. The consequences of not changing brake fluid for an extended period include reduced braking force, the formation of vapor lock in the brake lines affecting braking, corrosion of the brake lines, damage to internal valves in the anti-lock braking hydraulic assembly, and wear of the rubber cups and pistons in the brake master cylinder, leading to contamination of the brake fluid.
I'm totally qualified to speak on this. Last time at the repair shop, I saw a rookie pouring power steering fluid into the brake fluid reservoir, and the whole braking system had to be thoroughly cleaned! Brake fluid is used to pressurize the braking system and operates under extreme conditions, requiring a boiling point of at least 280°C; otherwise, it can cause vapor lock and brake failure during hard braking. Power steering fluid, on the other hand, is for making steering easier and operates at just 70-80°C. What's worse is their formulations are completely different—mixing them can cause rubber seals to corrode and swell. The easiest way to tell is by looking at the reservoir cap: a warning symbol (!) indicates brake fluid, while a steering wheel icon means power steering fluid. During maintenance, I always ask the mechanic to test the water content with a tester—if it's over 3%, it's time for a change.
Veteran driver teaches you the simplest way to tell them apart: look at the color. Brake fluid resembles diluted honey, typically light yellow; power steering fluid looks more like a translucent red wine color. Don't mix them up when buying oil at the supermarket! These two may look similar but have completely different personalities. Brake fluid is aggressive, needing to withstand high temperatures from brake pad friction; power steering fluid is much gentler, mainly serving the steering gear. If you mix them for convenience, rubber hoses can get corroded and leak in no time. My car's manual says brake fluid should be changed every two years, while power steering fluid only needs replacement every four years. The safest way is to watch closely during maintenance - the reservoirs are located on the left side of the engine bay.
With twenty years in auto repair, I encounter car owners who can't tell these two fluids apart every day. The brake fluid reservoir is near the firewall with a square cap; the power steering fluid reservoir has a steering wheel symbol and is mostly on the right. In terms of formulation, brake fluid must withstand high pressure, with DOT4 grade having a dry boiling point of at least 230°C, while power steering fluid operates at just 0.8MPa. Last week, I handled a case of mixed usage—mineral oil in the power steering fluid swelled the rubber cups in the brake master cylinder, causing the brakes to fail completely. Here’s a self-check tip: when the engine is cold, open the caps—brake fluid smells like alcohol, while power steering fluid has a faint oily odor.
