Re: Synthetic Oil for 5.7L Hemi
Synthetic engineoil does all the good things engineoil is supposed to do...better than dead-dino oil. So synthetics are 'oilier', have higher film strength, higher inherent viscosity index*, ozidize (wear out) much more slowly and hence last longer. What's not to love? Only the higher price, and even that is diminishing as DD oil prices increase faster than synthetics' prices.
My local Costco sells Mobil 1 in 5W20, 5W30, and 10W30 for $37/6 quarts regularly and at least once a year for $27 per 6-pack. I now have a half-dozen 6-packs under my bench.
To the OP--use the viscosity recommended by Jeep.
And BTW, it's not 'weight', it's viscosity. All engineoil weighs virtually the same. The 'W' stands for 'Winter'.
* the resistance to thinning as its temperature increases, thereby requiring less or perhaps NO VI-improver additive.