I had a post asking where you are. Depending on where you are located, 10-40 may be just fine. These numbers are for viscosity, how thick the oil remains at different temperatures. To need zero you would have to be in an extremely cold climate (sub zero). I am in SoCal and it is almost impossible to find 0-40. 10-40 works every bit as well for my climate. The key is synthetic such as Mobil One.

Chrysler lists 0-40 because they don't know where the car will be sold and operated.

Petroleum based oil needs additives to be have 5-30 have pour points (still pours) in the range of -30 to -40 deg F. These additives break down quickly. Synthetics do not use those additives and 5-30 naturally maintains a pour point of between -60 and -70 deg F.

If you want to read more go to: http://www.autoeducation.com/free_offer_thankyou

Bottom line is Mobil One is a great synthetic oil that will protect your engine. The viscosity rating is less important depending on where you live and operate the vehicle.