There is a good diagram in the Bentley repair manual.

 

I use this one I found on the Internet.

 

Thanks for the flow charts. Now they bring up a couple of questions. Sorry if these are obvious, but i'm new to this BMW engine.

I'm using a simple but large aftermarket radiator with only basic in and out hose ports. Can I eliminate or block the hoses as shown in my attachment? Will this cause any problems with coolant flow?

Radiator i have is a side tank cross flow radiator - like OEM. It is different in that the ports are reversed in position. Intake from thermostat housing is on passenger side like OEM, but low on radiator. Output to thermostat housing is on driver side but high on radiator. I can make up hoses that work. OEM is opposite with coolant input high on radiator and output low on radiator. Do you think there is any problem having the coolant flow across and up through the radiator and tanks, with gravity fighting the flow?

 

why don't you just get an oem radiator for an m54b30?

Sent from my LS670 using BimmerApp mobile app

 

Oops, I think I stated the difference backwards, but the essence is accurate. Flow would be upward.

This is a race car with no cockpit heater. Reason I'm leaning toward aftermarket is the cooling capacity for race track use here in the south. 90+ degrees on the track needs lots of cooling.
OEM cooling area is 17 1/2 inches tall x 23 inches across x 25mm cross section
Aftermarket cooling area is 17 1/2 inches tall x 21" across x 50mm cross section
Both radiators fit fine. OEM has about 90% more cooling area. There may be some loss of efficiency with thicker radiator but I would expect at least 50% more cooling capacity.