Here is a 16 page document dedicated to educating you on how the coolant system works, in particular related to the E30 and N54/52/55 engine.
This is a free download, just for you, PDF Format to view and enjoy. So read through it, understand what you may need to know. If you would like to take a bigger bite, feel free to buy the entire guide for either the E30 or the E36 chassis. Good luck and happy reading!!