I got an 88 750il a couple months ago and recently have deveolped a cooling flow problem. Thinking waterpump and replaced it. Still no flow after bleeding the system per instructions etc... When I took it apart I found the thermostat removed and the heater core bypassed. One side of the recovery tank "y" hose connected to rear header. I heard that the heatercore and valving MUST be connected??? Is this really true? Thermostat must be installed as well??? Any help would be greatly appreciated!!! Thanks in advance!