Even though the power steering system on the Porsche is a "sealed" system, you do need to change the fluid and filter as part of your service. The power steering filter is actually built into the reservoir and can only be changed by installing a new reservoir. Porsche 993s came with two different styles of power steering reservoirs; the early car's reservoirs were transparent with a minimum and maximum mark on the side. You would check the level by viewing the fluid between the marks. These reservoirs were replaced with black reservoirs with a dipstick attached to the cap. The transparent reservoirs are no longer being produced but if you are replacing a transparent reservoir with a new black one the new reservoir will come with the dipstick/cap included.
Porsche also changed the type of power steering fluid that they use in the system. Up until March of 1996 Porsche used Dexron II D ATF and for cars produced after March of 1996 Porsche switched to Pentosin (CHF 11S) fluid. These fluids can be mixed and you can add Pentosin to Dexron if you are topping up the system but both Porsche and Pelican recommend you flush, refill and bleed the system with Pentosin. Please see our article on flushing and bleeding your power steering system.
There are several methods to flushing out the old fluid but if you take it to a shop they are going to suck out as much old fluid as they can, top up with new fluid, run the motor and repeat until they have gotten most of the old fluid out and are happy with the color of the "new" fluid in the system. If you want you can disconnect the supply hose from the reservoir, attach an extension to the hose and insert it into a canister of fresh fluid and place the return line to the reservoir into an empty canister and start the motor. While this will work it can be very messy, it uses a LOT of fluid and can introduce air into the system from the supply hose to the pump. We do NOT recommend opening the lines at the steering rack in the front of the vehicle; cleanliness is important and you do not want to risk getting anything into the rack. Take your time and just suck out old fluid from the reservoir and keep topping it up and you will be fine.
If you are flushing and bleeding the system now is a really good time to check all of the hoses and replace as needed; please see our article on power steering hose replacement for additional instruction.
The power steering reservoir is located inside the engine compartment on the right side. You can probably get the reservoir out and the new one in by just removing the airbox lid but I like to remove the box (red arrow); it gives you a lot more room to work, some of the hoses clamps can be difficult to get to and power steering fluid is really slippery and messy and the extra room helps keep the mess to a minimum. Please see our articles on Varioram and non-Varioram airbox removal for further instructions.
With all the fluid you can get sucked out from the top removed, place a few rags under the reservoir (yellow arrow); even though you have removed the fluid some will still be in the bottom of the reservoir and spill out. Depending on whether you have an original reservoir or who replaced the one in your vehicle in the past you can find all kinds of differing hose clamps. Use the correct tool for your clamps and remove the supply hose (red arrow). If you want to attach these hoses into a clean supply of new fluid for the supply hose and the return line into an empty container and run the motor now is the time.
Install your new reservoir thereby replacing the filter inside it. The reservoir is held to the bay by a clamp that wraps around the mount on the inside (yellow arrow). Depending on how easy it is for you to get at the return hose on the bottom of the reservoir you can either loosen the clamp or remove it as we did to remove the reservoir from the mount. Remove the clamp on the return line (red arrow). Inspect the lines for budges, drying or cracks and replace as needed, Installation is the reverse of removal. Now fill the reservoir with new power steering fluid and turn the motor on for a few seconds and suck out more fluid and top up with new fluid. Continue these procedures until the fluid you are sucking out looks to the same color and consistency of the new fluid you are installing.
To bleed the system: Refill the reservoir and quickly turn the motor on and off; this will cause the level in the reservoir to drop rapidly so do not let the engine run long as this can introduce air into the system. If possible have a friend watch but do NOT let the reservoir run dry. Once you can start the engine and the level does not drop let the motor idle and turn the steering wheel quickly and at an even pace from lock to lock several times to bleed the air out of the system. Do not force the wheel when turning. Continue this procedure until the level remains constant and there are no more air bubbles in the system.