What is Power Steering Fluid?

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  • Written By: Mary Ellen Popolo
  • Edited By: Susan Barwick
  • Last Modified Date: 11 September 2019
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Power steering fluid is a hydraulic fluid used in the steering system of a vehicle. The fluid runs through the power steering pump and hoses, providing an assist to the steering system and making the vehicle easier to control. In addition to providing power to the system, the fluid works as a lubricant and a sealant to prevent corrosion and leaks in the system.

Although some fluids are water based, most are made from mineral oil because it provides better lubrication and can withstand the high temperatures and heat that the engine in a running vehicle creates. Other oils, such as rapeseed, canola, and silicone oils, are sometimes used for hydraulic fluids.

If a power steering system is leaking and becomes low on fluid, the difference will be noticeable when turning the steering wheel. The wheel may be more difficult to turn, and there may be a groaning noise. Spots of fluid collecting underneath the car can also be a sign of a leak. After filling the power steering fluid reservoir, the liquid may appear underneath the car, but this does not necessarily mean there is a leak; fluid on the ground could just be from overfilling the reservoir.


If the vehicle is low on fluid, adding more should make steering easier and eliminate the groaning noise when turning the steering wheel. If adding fluid does not resolve the problem, or if it only solves the problem for a short period of time, there might be a more serious issue with the power steering system. The power steering pump, valve, pulley, or one of the hoses might need to be replaced. Hoses often crack or become loose, causing a fluid leak.

The power steering fluid level should be checked at every oil change, and the entire power steering system should be flushed out, removing all of the fluid, every 60,000 miles (96,560 km). After flushing the system completely, new fluid should be put into the reservoir. Old fluid should never be re-used, and should be disposed of properly.

Although power steering, brake, and transmission fluid are all hydraulic fluids, they are not interchangeable. Putting the wrong fluid into the wrong system can cause serious damage. The products that are recommended for the vehicle should always be used.


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