2014 F250 6.7L PSD, 13.5K miles on Amsoil DEO Signature Series Max Duty 5w-40. 175K on engine. Donaldson filter this time. Sample #s 4, 5 & 6: Amsoil DEO SS 5w-40 Sample #s 2 & 3: Red Line 15w-40 Deleted 1K into #4. Interesting how iron tracks silicon. Switched it up and put Amsoil Diesel & Marine AME CI-4+ 15w40 in this time. And changed air filters. Will see how that goes.