I changed the oil last week in my 49 New Yorker; a few days later I changed the oil in the air cleaner. A few days later I took it for a drive; when I accelerated I left a smoke screen that would make James Bond proud! It did that several times, and had me quite concerned...and then I remembered this was the first time I'd driven it since the refill. I was low on 30w so finished off the half-quart of 20w sitting on the shelf. Between the viscosity difference and possibly overfilling it by a hair, well, it made perfect sense. With some driving it cleared up...sucked all the excess oil.