I've been looking at the Mobil 1 Product Guide, and specifically at the 0W-40 and 5W-30 ESP, because those are the only two products (plus 15W-50) on the list that are available locally. The 0W-40 has a Ford Service Fill Approval, but the 5W-30 ESP does not. I was looking at the HTHS viscosities of both, which are 3.5+ to meet specifications such as BMW LL. 5W-30 ESP is rated at 3.58, whilst 0W-40 is rated at 3.6. Despite being very similar, 0W-40 is FSF Approved and 5W-30 ESP is not. Neither oil is GF-4 approved, so that eliminates the possibility of FSF Approval being a WSS-M2C930-A certification. What exactly is FSF Approval, and would there be any issues with using 5W-30 ESP in a Ford engine, such as the Modular 4.6L? Thanks!