coolant leak 2h motor

[puttingau]

Hi, my 1980 HJ60 leaks coolant from a hole in the engine block just below the exhaust manifold. The hole is deliberately machined, but seems too small for a core plug, being about 8mm in diameter. It's the size of a bolt hole, about 25mm deep, but doesn't seem to be threaded. I've stopped the leak by tapering a stainless steel bolt and tapping it into the hole, but I'd like to know if this might be a dumb idea, and what is the purpose of this hole?
thanks for any help...

 

[tonytoyota]

Hi looks like it is the Engine drain plug on the side of the Engine below the manifold good look with it tonytoyota

 

[puttingau]

Hi looks like it is the Engine drain plug on the side of the Engine below the manifold good look with it tonytoyota

Thanks, I believe the drain plug is further down on the right, the problem leak is much further up, more central, right under the manifold. I have a picture, if it works, you can see the shiny bolt I have plugged the hole with right up the top...