CAFE fuel economy regulations were defined for trucks in 1979.

http://en.wikipedia.org/wiki/Corporate_Average_Fuel_Economy
I bet I could sneak into your garage during the middle of the night and change your oil to 5W30 and you would never know. And, your engine wouldn't either.

 

Your statement is meaningless. As I said, CAFE was unchanged from 96 to 2004, so there was no need to change oil for it, nor redo the specs for earlier years. They made the change for a reason, and it wasn't CAFE.

As far as changing the oil in the middle of the night, probably right, I would not be able to tell right then. However down the road if I kept on using it I am sure I would regret it, as I did with the 98.

 

Just wanted to share some info from a couple of Ford's Service bulletins:

TSB 01-4-7 actually mentions the reason 5w-20 in now recommended.

"ISSUE: Engine oil recommended for use in 2001 vehicles is SAE 5W-20 motor oil. This oil has an improved formulation to improve fuel economy."

Same thing when they switched from 10w-30 to 5w-30 a few years ago.
TSB 99-8-16 recommended that most engines use 5w-30. The reason being:

"Tests have proven SAE 5W-30 viscosity grade motor oil provides the optimum protection and benefits for Ford gasoline engines. At both high and low ambient temperature conditions, SAE 5W-30 provides the best overall protection. It allows faster starts under cold ambient temperatures.
SAE 5W-30 also provides approximately 1/2% increase in fuel economy over SAE 10W-30".

I've got 13 cases of 5w-30 stacked in the garage. I think I'll stick with it.

 

And as I stated, the 4.2 V6 clearances and tolerances were unchanged from 1996-2008. So, if 5W30 worked in 1996 it should work just as well in my 07 now in 2013.
When I can't find the oil I prefer at each OCI in 5W30 I use 5W20.
Would it offend you if I used 10W30?

 

Thank You Sir.
And, great choice on the 5W30.

 

It's your truck, obviously use whatever works best for you. But just curious, why are you pushing so hard for 5w30 if 5w20 is the recommended oil? I'm just curious of the benefit you're trying to achieve.

 

I switched my 05 5.4 to 5w30 junkie cam phasers don't make as much noise now lol yea they probably need replaced... I really don't see why this post got so big not like the user asked about 5w20 vs 10w30.. the oil isn't that big of a difference

 

I have been using Amsoil Signature Series 5W-20 & a Motorcraft Fiter only! Truck only sees about 5k miles a year so I only change the oil once a year in October.

 

The OP has a 4.2 V-6, which is an old tech pushrod motor. You can put just about anything in one of those and not hurt it. All you guys chiming in with OHC V8's are trying to compare apples to oranges. I have a friend that puts 20w50 in everything he owns and he has never had an oil-related failure.