I just bought a used 2013 Dodge Grand Caravan and don't have the user's manual for it, and couldn't find the information looking through the online version of the manual.
I have a 2010 Jetta that, when I got it (also used) was pleasantly surprised to find that synthetic oil is recommended that this increased the time between oil changes significantly. I couldn't find what kind of oil (conventional vs. synthetic) is recommended for the Grand Caravan and also whether using synthetic oil would increase time/mileage between oil changes relative to conventional.