I have a 1990 cylinder head that seems otherwise fine. It had the usual large carbon build up. However, Cylinder 3 has a pin point hole between the valves. Cylinder 4 has a pinpoint hole between the cylinder wall and the inake valve stem guide. In all four cylinders, the flat part inside the fire ring has numerous small cracks but all are short, in no particular direction, and are smooth to the touch. Are these imperfections in the aluminum head or beginnings of cracks?

I would agree that the aluminum head may have casting imperfections as a few do.

The process for casting aluminum heads can include small pockets of air, or voids in a poor, or bad, casting that can offen weaken the head especially if ever overheated. Also, you should not use green anti-freeze in an engine with an aluminum head as the PH level in green anti-freeze is very acidic and corrodes aluminum and interior water channels within the head.

Zerex makes an anti-freeze formulated for aluminum, also Mercedes Benz reqires all their engines use their pink MB anti-freeze, not sure if Volvo spec's that, but you should avoid green ant-freeze.

Steve...