When I put my turbo motor in, I went to replace the heater hoses, and found a plastic tee that looked like it was from the hardware store, along the right side of the block. On my 81, there are two outlets on the right side of the block, one goes presumably into the heater core, the other one goes to this tee which is also connected to the heater core outlet (I presume) and then onto the front of the engine. Well I wanted to replace this plastic tee I had in there. It was a 3/4 in tee, which made it almost impossible to fit new hoses on. Somehow the PO had gotten the original hoses over it, but I couldn't get new ones on. Well I go to the junkyard looking for a tee and find a zx sans head, that still has the tee init. It is a strange looking tee though. Turns out that it is some kind of pressure regulator. I think it prevents coolant from bypassing the heater core unless the heat is turned off. Well I put it in place of my plastic tee, and sure enough, it was broken and started leaking. The tee is made from brass but the pressure regulator part is plastic and is pressed in. Right now I am fixing it with jb weld, but I can see why it was replaced in the first place, many years ago. Using a regular tee seemed to work fine all those years, but I could not find a non-plastic replacement, that is why I went to the junkyard in the first place. Hopefully my jb-weld will do the trick and I will be back in buisiness. Mayb it will help the heater heat up faster, as it does take some time to get nice and warm on cold winter days! Sorry for the long story!