i have a 760 TI any thick grey white smoke is coming from the exhaust, is it a head gasket problem or something else?

You are probably sucking oil through the turbo seal. Is there oil in the air intake or intercooler pipes?

Did you try a compression test? No comp in any cylinder would mean blowby pressure is pushing pressure into the lower engine and squezzing oil out where it can.

This is often death,

Could be a head gasket, what does the smoke smell like? If it smells sweet it is a head gasket. You can also verify by opening your coolant resivoir and rev the engine a small amount. If you see air bubbles it's a head gasket. You will see water flow in the coolant tank but if it's air thats bad.

If the smoke is a grey with a bluish tint. It could be oil. I don't know about all Volvos, but turbos somtimes blow the seal that isolates the bearing from either the impeller or compressor. That will use a ton of oil and it will smoke like nobodies business.