Bleeding Power Steering

Power steering works by way of hydraulic pressure. Fire up some hydraulic pressure in something like a backhoe, and moving giant rocks around is as easy as pulling a few levers. A forklift uses hydraulic pressure to lift pallets full of concrete blocks high onto this shelf or that. This miracle of hydraulic pressure also makes a great deal of the everyday driving experience easier. Turning the steering wheel from left to right in a car or truck is effortless thanks to power steering by way of hydraulic pressure. Things that work by way of hydraulics have no room for pneumatics. Power steering systems are one of these things. Air can be compressed whereas fluid cannot. Air has no place in a hydraulic power steering system.

Full of Hot Air
If the usual effortless power steering experience has become noisier and more laborious then there could be some air in there. A sure sign of air in the system is what sounds like a mildly disgruntled cat under the hood. This growling will get louder during power steering intensive movements like parallel parking. The first thing to check when the power steering starts moaning and groaning is the fluid level. If topping off the fluid calms down the noise and returns power steering operation to normal then all is well. If the groaning returns a short time later along with fluid gone missing—then suspect a leak as both the reason for the fluid vanishing act and air entering the system.

Air From Where?
The usual suspect in power steering fluid leaks is the power steering pressure hose. In the process of fixing where the air gets in, it's easy to introduce some more. After replacing a power steering pump or pressure hose it's always a good plan to bleed the system of air. For most power steering equipped vehicles this is a simple process. Turning the steering wheel lock-to-lock several times will remove any unwanted air in there. In some more oddball machines like this Mitsubishi Starion shown here, the system requires a bleeding beyond the usual back and forth routine. The following are a few tips from the service manual and the miracle of the Internet.