'Tho I caught some static for it a couple of years ago, I've been using 5W-40 from the first oil change (until recently, as 5W is hard to find by me now).
Yet Another Oil Change Post
IIRC, 5W is good down to -20*F (check the owner's manual for the exact #).
It's funny how the "'engineers" now say OK to 15W-40 because it solves the whining problem that some owners experience. I wonder, if it was so important that we use 0 or 5W 2 years ago, what are we sacrificing by now using 15W to quiet down the squirters? Probably nothing, but its something to think about.
It's a dynamic world.
I added a 1/2 pint of E.O.S. (as described in my earlier post) to my oil. I'll stock up on 5W-40 diesel next time around.
-Steve