[m5james]

While likely not necessary to replace the expansion tank, I removed the fender liner since at the time I was wondering of maybe the shock had blown out due to all the fluid everywhere and even though I found nothing on the shock itself, I couldn't source where this yellow fluid was coming from. Needless to say, this was kind of a bitch due to space and BMW uses rivets to attach the fender to the liner, which I've replaced using normal expansion rivets.

Without thinking about it until after I'd found the crack, said fluid was simply Zerex G-05 coolant, which I've used myself in the past since it's available locally, cheaper than BMW coolant and is still phosphate-free, something that prevents us from using all makes all models coolant

Having all this apart made it much easier to very access to the plugs on the bottom of the expansion tank and remove the hose on one of the electric water pumps. This location also helped to drain the coolant from the block, radiator(s) and a straight shot into my bucket once I turned the key on (engine still off) and flooring the gas pedal for 10 seconds, which in turn causes the electric pumps to turn on in order to self bleed the system. Last but not least was the hose that is on the bottom of the radiator that feeds to another smaller radiator in the drivers side lower grill opening. Oddly these radiators have no petcock.

Once drained, I blew out whatever remaining coolant I could using compressed air at the 5 locations I had dangling and open. I reconnected everything and poured in the Evans Prep Fluid. For the record I didn't do this on my E53 since I was able to find the blocks drain bolt but I couldn't find one on the E70. I ran a gallon of that around the system to flush out as much of the old coolant as possible then redrained everything again.

I was never able to find something stating our total cooling system capacity so I played it save by getting an Evans four pack off eBay for $160 shipped...1 gallon of prep and 3 gallons of coolant. I ended up using about 2.5 gallons of the coolant itself, so hopefully that means I did a good job of draining out the old stuff. It's only been a day but it's good to go so far.