4-5K with the same oil Ford uses but since you can't find the Ford branded Kendall I just order it. $5 a qt. at my door. Ford could have used any oil but they chose the only one with titanium for good reasons. You can find test results at the National Lab, NIST.GOV and see what Ford saw.The titanium additive works in Kendall GT 1. Patent has run out and now Mobil, Pennzoil and Castrol have it. So any full syn with titanium and the Ford Fl400s filter. Also rotate the tires at the same time!
Or pick your fav......we all have one! There are no "bad" oils that meet Ford specs.