Trying to see if my current generation was designed with 5w-20 in mind or was it caught up in the "administrative decision" to use 5w-20.
(read in between the line) I'm trying to justify switching to 5w-30 in New Orleans summers and traffic jams.
thats because of the backspecing. you can still use the 5w30 that you have been using.
iirc the only engines that were not backspeced were the 4.0 v-6 and the 3.9l v-8, this also applies for the current versions of these engines.
Here we go again.
The 5w-20 has been designed to improve fuel economy, according to FoMoCo itself.
You can freely go from 5w-30 to 5w-20 and back.
The only exceptions are the 3.3L in the Villager, the 3.9L in the Lincoln, the 2.0L in the Focus SVT and the 4.0L in the Ranger and Explorer.
Basically it comes down to this. Engines spec'd originally for Ford spec'd 5W-20 are most likely better off using that rather than a dino 5W-30. While I'm a proponent of "thinner" oils I also believe pushrod engines are better off with "beefier" oils such a 10W-30. A 5W-30 dino will become a poor "5W-20" or less oil in less than 2000 miles usually it seems. For OHC engines I'd use 5W-20 oils in a heartbeat if I was using 5W-30 dino's. For my 1996 Ford Contour 2.0L Zetec I do continue to use Schaeffers 5W-30 Supreme Blend oil. But again if I was using a dino 5W-30 I would definitely switch to a Ford rated semi syn 5W-20.