If this was gasoline engine i'd say.... valve seals, where oil seeps into combustion chamber when engine is stopped - then burns off while starting. Takin foot off gas pedal might pull oil into chambers too through bad oil seals.

Otherwise, my '79 240D 112k does the same thing at starting..... especially visible in cold weather - makin me think its unburnt diesel fuel.

Am new to owning diesels, interested in what the forum thinks.

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'80 300SD/ w116
'79 240D 4-spd
'71 750cc Guzzi

previously owned:

'83 240D 4-spd
'77 280SEL 4-spd
'74 280/8
'72 250/8
'65 220Sb 4-spd
'63 220Sb 4-spd
'63 190c 4-spd
'61 220Sb 4-spd
'60 190b 4-spd