For the first 13,000 miles I ran Mobil 1 EP 5W-30. On the last OC, changed to Chevron Delo 400 XSP 5W-40 which is a dual rated oil, gas and diesel, and is also SN+ rated to address any LSPI issues. The 3.5 Ecoboost was smooth running with the Mobil, and is smoother still with the Chevron. I'm not particularly concerned about fuel dilution in the 2nd gen ecoboost because of the dual injection system; direct injection is only used on starting and when the driver asks for significant power with the right foot. At all other times, port injection is used, keeping intake ports clean as well. Keeping with 5000 mile OCI's as well.