Those 2002 owners who flush their cooling systems frequently may have to replace the center tie-rod of the steering system prematurely. With the car's wheels pointed straight ahead, the cooling system drain plug lies directly above the ball joint that serves as a connector between the idler arm and the center tie-rod. During the flushing procedure, hot caustic water has a tendency to wash the grease from the ball joint (the seal is poorly designed I want my money back!). Over the long run, the resulting high friction causes galling and eventually the ball ends up three sizes too small for its joint, resulting in slop. If you've noticed a strange clunk when hitting a bump, especially if the steering is hard to port or starboard, check the center tie-rod. Your local BMW parts man will be glad to see you.
The best preventative is to use distilled water and a good antifreeze, and flush every other year. When flushing, turn the wheels full left to move the ball joint out of harm's way.
Author: Art Skinner