I'd warm it up first (full operating temp too)..
When the oil settles at the bottom of the pan, all the contaminates and 'sludge' form down there too and won't drain out when it's cold.
You'll get the bulk of the cold oil to drain, but it'll leave whatever has settled to the bottom of the pan on the bottom of the pan...
I used to drain cold oil and the new oil would turn 'dark' again pretty fast.. Started doing the warm oil drains and after a couple of changes, the new oil would stay 'cleaner' longer...
Just my experience with it and no 'scientific' proof what so ever.. Just what saw the color of the new oil did... ;)
Good luck!
Mitch
