Maybe someone else can correct me on this but if the risers or manifold were cracked wouldn't they leak back on top of the Pistons and hydrolock the motor? I understand they could eventually get past the rings but first would they not go there?
Yes they could.
But you generally don't have more than 2 ex valves open on one side, the amount of water that could get in there is small, it doesn't all leak past the rings and if you were running the engine after, for very long, the water would evaporate quickly.
I had that very same problem on both sides of a V-8. It hydrolocked every time I shut down and then tried to restart after less than 10 min or so. (like to pick up a skier)
If I waited more than about 30 min or so, or overnight, it would restart normally (indicating that the water leaked past the rings after about 30 min.) I never had enough water to appear milky.
When I pulled the heads, 1 piston on each side had evidence of water that had sat on top of the piston for quite some time. I never had milky looking oil at all though
It's unlikely (even with both risers or manifolds leaking) ..... you would get enough water in the oil after a shutdown make it "milky"
You should pump the block up to 15 or 20 PSI, close the supply valve (the gage is on the engine side right?) and disconnect the air supply. Let it sit (compressor OFF so you can hear) and put your ear up to the oil fill, and near each sparkplug hole and see if you can hear anything.
Even try putting some soapy water on the intake manifold where they bolt to the head and see if you see bubbles.
If there's no leaks, the engine should hold pressure nearly indefinitely.
Let me also add that if the block is actually cracked, it might not leak when cold as much it would leak if hot (or at normal running temp)
