BMW with Nissan 6

Hello, I have a loss of water in the engine, and not C if it is from the pump or that, it is not of any mangon, since I review them all, the issue is that I want to disarm it, there is some manual or video or something that guides me a bit, it is a BMW with a nissan engine of 6 diesel cylinders is the D I think the one with chain, of course thank you very much !!!