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Join Date: Feb 2008
Location: United Kingdom
OK so the cars a Fiat and this is an Alfa forum, luckily this is the same engine as the 1.9 16V JTD so I'll answer your Q's.
The smoke could be from any cylinder or turbo related part, that includes, valve stem seals, head gasket, injector, piston rings, turbo bearings, any blocked breather, a stuck CLOSED EGR valve, split inlet hose, split intercooler or cracked head. TBH if the smoke stops after a few seconds I wouldn't be worried, but the most likely seals to be leaking and causing this are the turbo bearing seals, apart from the head gasket tey are the hardest working seals on the car.
The difference in temperature is probably just making the seals remain more plyable during the summer warmth when the engine has cooled, in the winter as the temperature drops seals will also contract and allow oil past in small ammounts, it's no problem as this is why emmisions are done on the engine when it's at running temp.