black smoke from exhaust when start in -35 temp

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Happened one very cold morning, very black but cleared within a min and when started later in day, the weather had warmed it was ok. The oil had been changed a week prior with 5w40, I had neglected the oil change for a year . The weather had been extreme cold for amonth, I do not have a block heater, it starts well. Since then it has abit of black smoke just one morning when it was cold. I noticed a bit of yellow drips under what seems to be centre/front of vehicle a while back have not noticed anymore.