Jeronz: Power Steering Fluid Change Procedure
 

My notes from my recent p/s fluid changes.

Power Steering Flush E36M3 E46
E36M3: Remove air box to gain access to the reservoir.

Open reservoir and siphon the fluid out. Prepare for spillage and pull the inlet and outlet hoses from the reservoir. The OEM clamps are tricky and require a flat head screwdriver to unclip. Replace the OEM clamps with worm clamps.

Remove the reservoir by loosening the strap around it. Use a small Torx bit to remove the screen retaining screw inside the reservoir. The screen will be loose inside the reservoir but it is too big to remove. Clean the reservoir and cap with engine degreaser and a hose end sprayer. Dry it thoroughly then reattach the screen.

Put a small piece of plastic bag over the small reservoir nib and secure it with a zip tie or rubber band. Replace the reservoir and attach the large hose but not the small hose.

Route the small return line to a catch container instead of the reservoir.
E36M3: The return line will pivot on its lower connection and twist down into a standard 5qt ATF or engine oil jug.
E46: I used a medium sized piece of hose that friction fit on the outside of the return line.

Fill the reservoir with new ATF. It holds about ½ qt. Run the engine for about 15 sec and it will drain the reservoir and empty into the catch container. Check the fluid in the catch container and empty it. Repeat until the fluid is clean, approx 3 quarts. You can leave the top off the reservoir and continually fill it while the engine is running if that suits you.

Notes:
The hoses tend to form fit around the barbed reservoir nibs and can be nearly impossible to remove. A hose puller might work if you can find one large enough.

On my E36M3, I had to remove the outlet hose at the pump and take the reservoir out with the hose attached. I tried holding the reservoir with my feet and pulling the hose off but the reservoir nib broke off so I had to replace it. I also replaced the two crush washers where the hose banjo fitting meets the pump, but they were probably reusable. I just crushed the remains of the reservoir that broke off in the hose with a hammer and reused the hose. All of the pulling and movement on my outlet hose caused it to later leak a the lower crimp. The inlet hose was hard to remove too but I got it by hand. I managed to get both hoses off my E46 by hand.

Thats very helpful.
I read on some web site that the power steering pumps on some BMWs have a drain plug, but aparently not on the recent models. Bentley for E39s does not mention it.
If one does not want to detach the hoses from the reservoir, perhaps the same result could be achived by running a drain hose directly through the reservoir (after unscrewing the filter plate) into the return line.
I suppose also that the whole thing could be done iteratively as well: just keep emptying and refilling the reservoir, drive 50 miles, and repeat until the fluid is replaced.

The filter screen is larger than the mouth so it will not come out of the reserviour.

The inlet line connects to the pump very low so you could pull this line at the pump to drain the pump.