Cylinder head cracked around spark no.4

[Nassa]

hi guys, I'm from Australia and driving vectra c with z22se 171k km I have mini cracks around spark plug no.4.
I would like to know how long it takes the head for a complete failure, and is there a solution before the cracks reach the water channels?
coolant still clear oil fairly clean after 1000km (rings I believe), Im changing it every 3 months or 1k km (10w40) full synthetic.
car has new GM chain kit, pcv cleaned, new spark plugs, new valves seals
compression test 180psi on 1,2,3 and 178psi on 4.
Oil consumption 0.8 - 0.9L/1000 car drives ok.
And it's not because I'm over titting the plug I use the right torque specs I believe it's a deffect in the design.

 

[vocky]

there are 'casting' marks at the bottom of the spark plug hole, which can be confused with cracks.

When the head cracks it leaks striaght away, the alloy is so thin that it cracks striaght through.

 

[corsaZ22se]

I will second what Vocky says.
some tuning company "checked" mine before mapping it. only trouble being the engine was a full temperature after a 100+ mile drive down there.
Right royal numpties! started loosing coolant slowly with in days.
Only fix is a new head as far as i know?

 

[Nassa]

Thanks vocky, here is some photos of the head recess

 

[Nassa]

Cylinder number 4 is the first one.

 

[ob one]

I had a cracked head on cylinder 4 when the spark plug was in it would fill up with water