zz 7 L" ~9 m& _+ c/ Y# E* l# B, DTypically engine Manufacturers specify 10W-30 lubricants down to around -15F and 5W-30 lubricants to around -22F. These are continuous temps so spasmodically below a little won't be an issue. As others have alluded to though it may "test" the battery and starter a bit!