Okay, just to really muddy the waters regarding the proper Motorcraft oil filter, on the Ford parts site to which BlueBomber links, one finds three parts listings for Fiesta oil filters. Under "part number", all three are given the number 6731, but they differ in what follows/is under the part number in parentheses. The first is 6731 (FL-2050), and is listed as being the part for the 1.0L EcoBoost engine. The second is 6731 (FL-910S) and the indication is that this part is for the 1.6L TIVCT PFI Sigma. Finally, one finds 6731 (FL-2057) listed as the oil filter belonging to the 1.6L EcoBoost SCTi 160/182PS-Sigma. So, all three have the same part number, followed by differing bits as parentheticals. My hypothesis as a starting point would be that any of the three can be used with any of the three engines, though they'll have different performance characteristics and will need replacement at different intervals. Second would be that the Ford Part inventory personnel made what I consider a boo-boo by giving all three the same basic part number and trying to differentiate with the parenthetical numbering. That's the sort of thing that just begs for mistakes to be made, so I hope that's not it, but who knows. As it stands now, the only one to give me a warm fuzzy would be the 6731 (FL-2057).
Please help me out here, o ye with greater knowledge: Am I crazy, stupid, or just uninformed?