i ask a mechanic and he has told me something about the seal of exhaust system, well i will put a image in the next postIdeally a cylinder compression test followed by a cylinder leakdown test would give an indication of headgasket/valve stem oil seals/etc. You could follow it up with pressure testing the cooling system as well.
I know diagnosing remoting is usually a disaster but it sounds like the smoke associated with a cracked turbo exhaust housing. Coolant weeps into the exhaust and is burnt off usually whilst sitting at traffic lights or left idling for a short time. Might be time for a turbo upgrade..