As I said in one of your other posts, I don’t know if there is any interface between the turbo exhaust/intake system and the cooling system. If there is, someone else will have to tell you about it since I never worked on one. Coolant to air aftercoolers are common on large trucks, but think Volvo is air to air. I also don’t know about the oil cooler to coolant interface, but I don’t think that relates to the combustion chambers.

With the above caveat, the loss of coolant doesn’t have many places to go. It can come out where you can see it (such as leak out on the ground or get pushed out the overflow tank), it can leak into the cabin onto the floorboards from the heater, it can go into the transmission through the trans cooler, it can leak into the crankcase, or it can go out the tail pipe. If it goes into the trans or crankcase, the oil/ATF will get milky.

You have already said several times that the combustion gasses are bleeding into the coolant system, and that the coolant system is overpressured, and that you have overheated the car several times.

These are all textbook classic signs of a blown head gasket, unless you are unlucky, in which case it could be a cracked head or block. If you are getting combustion gasses into the cooling system, it is possible that on shut down you are getting the cylinder filled with coolant. This can cause a hydrostatic lock, which in turn may bend a connecting rod when you hit the key. If you insist on starting/driving the car instead of fixing it, you should pull the spark plugs out and crank it over to push the coolant out before starting it.

Can anyone else think of a reason not to pull the head off? You may want to read the other 3 or 4 posts over the last few days on this issue before you decide.

Charley