Originally Posted by dan50
Any oil that meets Ford spec WSS...945 (see your manual) is fine. And Mobil1 5w/20 is one of those.
There are precious few synthetics in the US market based on the old definition of a synthetic, Amsoil being one. However, Mobil, Valvoline, most Pennzoil, Quaker State, Castrol, etc. synthetics are made out of crude oil subject to extra steps in the refining process. They are of higher quality than conventional oils and perform better in extreme conditions and are capable of longer oil change intervals. So is Mobil1 as good as a "true" synthetic? Just about, and at an affordable price.
To clarify, if we check the websites of the oil companies mentioned above that are manufacturing the cheaper Group, "III", what I call the pretend-it's-a-synthetic oil, (which are merely refined from petroleum crude oil and not manufactured using the superior performing synthetic oils using Group IV PAO or Group V ester base stocks), we find the recommended drain interval is no longer than the even cheaper Group II petroleum oils. For any oil to be safely capable of the rigors of extended drain intervals, the oils additive package has to be specifically formulated for this. Matters not what the base stock of the oil is. The additive package and a high TBN, (total base number), are what is necessary for safe extended drain intervals.