Hi there,
My suggestion is to run it awhile and see if the white smoke goes away. If it doesn't, check the coolant - is it going down?
Normally if there is a leak into a combustion chamber, there will also be a compression leak back into the cooling system, which will cause lots of bubbles in the radiator cap overflow. Are there continuing bubbles when you remove the cap?? Sure sign of either a bad head gasket or a crack in head or block!

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C