Power steering fluid is the hydraulic fluid that flows through a vehicle's power steering system and provides the transfer of energy from one hydraulic cylinder to another. By doing so, it allows the vehicle to utilise hydraulic power to make the vehicle easier to steer. Though modern power steering fluids may last the life of a vehicle, the fluid should be replaced when it becomes contaminated.
All the components of a power steering system will degrade over time, if only slightly. As metal rusts and o-rings degrade, they release tiny particles of impurities into the power steering fluid. As these impurities build up, they can begin to clog the power steering pump and speed up the corrosion of the components within the system. Ideally, the power steering fluid should be replaced before this is allowed to happen.
The best test of whether or not power steering fluid needs changing is a visual inspection of the fluid's colour. Fresh power steering fluid is usually orange, red or pink and somewhat transparent, whereas contaminated power steering fluid is black, brown or impossible to see through. A vehicle's power steering fluid colour can be checked on a dipstick found beneath the hood.
Automotive manufacturers have not always recommended scheduled maintenance intervals for power steering fluid, though some have adopted this practice. There are some high-mileage formulas of power steering fluid that are designed to last the life of a vehicle, so if a manufacturer uses this fluid in its new cars, it may not recommend a maintenance interval at all. If there is a recommended interval for changing a vehicle's power steering fluid, it will be printed in the owner's manual. When the owner of a vehicle replaces the power steering fluid according to the schedule, she should defer to the maintenance instructions given by the manufacturer of the fluid used in the replacement.
A vehicle's power steering fluid can be completely drained, flushed and replaced, but this is not a simple maintenance task. The biggest challenge is that the vehicle must be level for proper drainage, so a hydraulic car lift must typically be used in place of a light-duty car jack. Total replacement of the power steering fluid is often performed by professional mechanics using a hydraulic lift and other heavy-duty equipment.
Vehicle owners can gradually replace their own power steering fluid over time. First, they must make sure they have the specific type of fluid recommended by the auto manufacturer. Then they must open the bonnet, open the power steering fluid reservoir and extract as much power steering fluid as possible using a syringe-like tool called a transfer tool. The reservoir should then be topped off with fresh fluid to the fill line. It is best to then start the car, turn the wheel a few times and then reinspect the fluid level, because turning the wheel can cause the level to settle a bit. By doing this once a week for a few weeks, vehicle owners can make the fluid cleaner overall without performing a total replacement.