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.
The only way any oil, (regardless of its base stock), is safely capable of extended drain intervals is if it's specifically formulated for the rigors of extended drain service. If we check the drain intervals of the so-called, "synthetic oils" mentioned above, we find they are precisely the same as their dead dinosaur/petroleum oil brethren.
The, "old definition of a synthetic", millions feel is the correct definition. German motorists don't like being deceived, or played for fools and in Germany it's illegal for any Group III oil to be termed a synthetic oil. At least the Germans have it right!