I have a 1985 BJ60 that came with a very strange addition to the cooling system. The rear heater in this car was disconnected for some unknown reason (not leaking or clogged) by one of the previous owners and I wanted to reconnect it again. However, when I attempted to do this, I became extremely confused. The front heater is connected as it should be (I think) - from a port at the back of the head - through the valve - through the core - and then to the pump inlet (bypassing the T-connection for the rear heater in this case). The rear heater is fully disconnected. Now for the strange one - an additional hose goes from the rear block drain (impossible to get to) to the front of the head. It is mostly off-the shelf hose but it actually uses a section of the steel return line that was originally for the rear heater. This modification looks extremely deliberate and I am at a total loss as to why it was done. The only thing I can think of is maybe it was intended to make the engine run hotter, because as far as I can tell, this line is basically short-circuiting the cooling system. I drew a diagram showing how I think the cooling system is supposed to work (with the additional line showed as a dashed hose). I also tried pinching off this line and driving around, but I didn't notice any difference. Please let me know if you have any thoughts on this or if you see anything wrong with the diagram, I'm hoping that maybe I'm just not understanding how it works correctly.
