Air Compressor air in coolant.

[Wiseman]

The head is two halves. Two pieces or whatever you want to call them. There is a gasket in between them looking like a maze/labyrinth. It seals air and coolant passageways keeping them separate . There is where the leakage occurs in one or other direction.
That’s it . No magic. No science . No nothing. Just trouble .

Now , get your favorite drink, favorite cigar, have a comfortable seat and say:
- f$%k EVERYTHING! and relax