What motor oil is best to use in cold winters?

My neighbor says it doesn't matter. I beg to differ. I am currently using 10w40 but is that good for the engine if the weather hits below freezing?What motor oil is best to use in cold winters?
the number in front of the W is the thickness of the oil. The hotter it gets outside the thicker the oil needs to be so it doesn't completely break down when the engine heats it up even more. On the same note the colder it is outside the thinner the oil needs to be because it can't really coat all of the moving parts if it is to cold to move around. The lower the numbers the thinner it is. The first set is its thickness cold, then the letter W, and the second set is its thickness hot. The owners manual should tell you what type of oil to use depending on the yearly lows of your area.What motor oil is best to use in cold winters?
I really feel that using a good quality full synthetic oil like Mobil 1, Castol Syntec or Penzoil Platinum is the best thing. As for the ';weight'; of the oil, you should use exactly what the manufacturer specifies in your owners manual. If it says use 10w30 in your book, use that. Some people go with a thinner oil in the winter, like a 5w30. The idea is that in colder temps the thinner oil will get circulating faster resulting in less wear. That should be fine too. It's not much of a difference.
thinner oil in the extreme cold! thicker oil takes longer to heat up %26amp; lubricate properly which could result in premature engine failure!
how cold is cold any thing above -15 deg your good with 10w40. if you live in alaska go to 5w asap or live some wear that cold every day all winter long and colder.
it depends on the engine. older pushrod engines can handle 10w30 ok. newr ones that are overhead cam should get 5w30 for cold temps. look in the manual
just use 5w30