Edit: I swear there was a post asking about the bleed procedure. I don't know where it went. Anyway, here the answer to that phantom question:
Are you asking about the beginning drain of old coolant procedure or the post install bleed with new coolant? Here are both:
Preinstall drain: what we did first once we put the car on race ramps and connect it to a battery charger was open the radiator drain plug. I should mention if you have just driven the car a distance you should give it a cool off time we waited 45 minutes as we went and bought a big tub to collect the coolant (advanced had a nice big one for 10 bucks). Let the coolant drain from the radiator drain then start the removal of hoses. Be sure to have your collection pan ready there is a lot of coolant in those parts. As soon as you think the part is empty more comes out.
Install: same basic procedure as the e90 but much easier from what I understand. (My buddy has an e90 so we will be doing it sometime soon, I'll look up your DIY) everything is easily accessible and there is no need to move sway bars or anything like that.
Bleed: once everything is installed and hoses reconnected the fun begins. We did this wrong twice so learn from our mistake. Here is where the battery charger is essential since you will be running it solely on battery for the 12 minute procedure. Using a proper coolant bleed funnel isn't totally necessary but it helps (my buddy had just purchased one so we used it, here is a link if you want one or just want to see what I'm talking about
:
http://www.bavauto.com/fland.asp?part=24680) Pour as much coolant (50/50 mix with distilled water) as it will accept in the expansion tank.
The overflow valve is underneath the plastic shroud at the front of the engine so you'll need to remove that. It just a handful of screws. Open the valve. Now in the car turn the key to the point right before you engage the starter and crank. (Do not crank the engine!) On the air conditioning set the heat to full and the blower to the first notch on. Depress the accelerator to the floor for 10 seconds then take your foot off. If you listen you should here the water pump whir. You'll get coolant numbing Ana's the coolant from the expansion tank drains into the system keep adding more until you start getting coolant out of the overflow valve. The procedure lasts 12 minutes. It isn't fun but doing it right the 1st time saves a lot of headache. I know, here comes story time!
So what did we do wrong? Nothing until the bleed procedure. We couldn't tell if the procedure initiated (listen be patient, you'll be able to hear the pump). Well we weren't patient so after 3 attempts to get it going we we put back on the expansion tank cap thinking thinking that was the issue (also we had not opened the overflow valve) after 3 attempts we heard it going (still cap on not adding coolant as necessary) once it completed I took it for a test drive. It took quite some time to get to operating temp (longer than usual) and the heat was not not hot, at all. Worrying. I was on my way back when the temp gauge started rocketing toward red (if you want terror, watch a temp gauge climb like a bat out of hell, it's pants discoloringly scary). So immediate dive to the side of the road and shut her down before the red. Buddy comes and we add coolant. The issue was bubbles in the system, yay!
So we refill then limp home. We do the procedure again, still the wrong way, and drive it. No temp change but low coolant light. We finally get it sorted after 2 hours. No lights, severing heat, no needle move from straight up and down. Happily our local Indy shop owner (Todd at Bavarian Repair I'm Woodstock, GA) invited us over from a cookout at his shop. We eat he checks out our work and when we explain the issues withe the bleed procedure he kindly offers to take a look. We run through the procedure again and we discover our mistakes (not opening overflow valve and not adding coolant as procedure ran) he does it correctly and while we eventually got it right I now have peace of mind a mechanic looked it over and said "Das ist gut". And best of all no charge for his time. I bought the parts from him and he was happy to give me peace of mind.
Learn from our mistakes do it right the first time and it will be super easy. Do it wrong and you'll end up driving in 90 degree weather with the heat on full blast crapping your pants at a rocketing temp gauge. Good luck!