I just bought a 2015 Jeep Cherokee and the recommended oil is 0w-20. This is the first vehicle I've owned with that viscosity. The vehicle I traded in used 5W-20 and I have about 6 Litres of 5w-20 Penzoil Platinum leftover. Not sure if I should use that sometime down the road on this vehicle or not. By the time the first oil change arrives I'll probably stick with 0W-20 as cooler temps will be in my area by then. The owners manual recommends Mopar 0w-20, or Penzoil or Shell Helix . My salesman told me that these vehicles now use synthetic oil. Does the 0w-20 motor oil spec automatically make it a synthetic oil ?, whereas 5w-20's could be found in both conventional and synthetic oils ?.