Hey Jess!
Since I happed to be refilling my radiator yesterday I checked the BMW coolant label for mixing coolant and distilled water. I had always used a 1:1 mix of BMW coolant and Distilled water and perhaps I shouldn't have.
The way I read it at least this coolant is made to cut down 60/40 or 50/50. The label also confirms BMWs recommendation of not mixing coolant types as they may contain phosphates.
I see the premixed coolant at the autostores going for $12 or so per gal, so a 50/50 mix of the $24 BMW stuff, 1 gal BMW AF plus 1 gal distilled water=2 gal, refill quantity) is still perhaps a little more cash wise, but does not contain phosphates and and in some cases, as in my Zionsville aluminum rad on the 540it, is required to be in warrenty.
Thanks for the rad cap removal clarification. Yeah, don't remove when hot. I have however bled via the bleed screw when at operating temp as the Thermostat is typically open and the system can pass excess air at it's high point. Old school from the M30 motors.
However, rereading the Bentley, you are right. Use the bleed screw when cool, closed when hot. I guess I've been lucky in the past. I can be taught...
Thanks!