Did alot of searching on how to flush the power steering for the e90,
the best I could find is this:
http://www.dvatp.com/bmw/diy/power_steering_flush/
Doug was specific on e36/46, and explains what the pros/cons with regard to each style.
My way:
-I chose to do this with the engine off (because I don't want a messy garage floor)
-The drain bolt is on the rack not the PS pump. I believe I found the true drain bolt (on the rack vs on the pump, see pics below).
I noticed that all the other bolts had really shallow heads (more chance of stripping/rounding them off.)
-There is no need to cover the pump or serpentine belt!
Tools needed:
8mm socet
19mm socket
torque wrench
Brake cleaner
Jack stands (not ramps)
Jack
Fluid:
1Lt of Pentosin CHF-11S (no substitution)
Steps:
1. raise car,
2. secure jack stands underneath the car so that the front wheels are free to turn
2. remove under carriage cover.
3. identify steering rack drain bolt.
(The one on the top, 19mm, black with the thicker head)
4. loosen the drain bolt (don't forget to place a pan under there)
5. uncover the reservoir
6. Turn the steering wheel lock to lock, repeatedly untill all the fluid drains out. (you could probably add fluid to the reservoir as it drains, so you can minimize air introduced into the system but I'm uncertain if you would just be draining new fluid out in the process, CHF-11s is not cheap!). according to Doug, the ps system is self bleeding.
7. close the drain bolt and torque it to 22 ft lbs. (not sure if this is right for this bolt, I'm just taking this spec from my experience with Honda's).
8. fill reservoir with new fluid, turning steering wheel lock to lock, to get as much as possible back into the rack (I drained 800 ml out) so try to get as much back in before you turn the car on to have the pump do the rest.
9. Lower the car after you put everything back. Turn on the car for 3 seconds and turn off, check the level and repeat till the level is good.
-allmotorh22