What is this part which my coolant is leaking from?

I have a 1985 Plymouth Volare slant 6, 225 cu. engine. When I poor water into the radiator it almost immediately starts pouring out ALL AROUND THE GASKET AREA of another component which seems to be in front of the engine block. One of the wheels the belts (in the front area next to the fan) wrap around is connected to this component. The 'component' seems to be a big steel 'cap' of some kind (its about a foot tall and wide and has bolts holding it to the engine block or something. The water pours out ALL AROUND the gasket area these bolts are supposed to be tightening. I had coolant leaking from a hose and when I tightened the screw on this leaking hose, a day later this mive leak appeared, could there be too much pressure or something which blew out this gasket? IT IS NOT THE WATER PUMP. I've replaced this before and I know what it is. Of course its not the alternator or the compressor either, both of which have wheels connected to them of their own which the belts go around.