I am wondering what weight oil I should run in my 2001 dodge 6sp H. O. I go up to Canada in the frigid temps of sometimes around 20 to 30 below ferenheight. I run 15w40 normally and have always since i've had it new, but when I start it up there it crankes over pretty hard after that oil has set for about 3 to 5 days in those temps. Should I just keep running the same weight oil or should I change to something else? Thank you.