I enjoy helping my friends change their oil.....can't u guys tell? My friend has a 98 Stratus with the 2.4L engine. It has 98K miles and he is taking this vehicle to Texas Tech University in Lubbock, Texas. It will be driven 20 miles every day. It is an 8 hour drive there. The owners manual states 10W30 from 0F to over 100F with 5W30 well below 0F and up to 100F. He has been using 5W30 since he purchased it but he has been using the incorrect viscosity for the temperatures that Chrysler recommends. Should I keep him on 5W30 or move him up to 10W30. It rarely, if ever gets below zero up in the panhandle. It gets close but I don't recall a time where it has.