Stop the presses! $15! LOL. I spend that on beer and wine every night...
Really though, running two weights would mean you have to time changes with the weather. Not quite worth that massive savings. Plus you loose having full synthetic. Not even close to being worth 15 bucks to me...

 

My OA with the factory 10-30 was way worse then the 15-40WT I normally run.

 

Eh, to each their own. The fact that it's full synthetic or otherwise means very little to the engine. All of the CJ-4 oils do an outstanding job; your engine really could care less exactly how the oil is made.

Of course it was, I'm sure your wear metals were sky high. Probably would have been just as high if they had used 5w40 from the factory as well.

 

I wonder why Ford says use 5/40 for extreme use if it doesn't offer better protection year round? Maybe they don't know what they are talking about? Silly Ford....

 

I wonder why they specify 10w30 for normal usage? Silly Ford.

 

Um, I never questioned 10/30 for normal usage. You, on the other hand, DID question the advantage of 5/40 for heavy all season usage. Ford doesn't say severe cold usage. Just severe which can be anytime of the year. 5 for when it's cold and 40 for when it's hot. With most guys here climbing under their trucks once a month to do unnecessary fuel filter drains, I'd think they'd opt for the extra $15 bucks worth of protection a couple times a year during oil changes. But like you said earlier, to each their own...