Until recently only the US has the technology to manufacture 5w-20 base oils. Austrailia just started making it in the last few years and I think you will find 5w-20 now speced in some Austrailian vehicles.
Your owners manual calls for 5w-20 in Canadian vehicles too.
Scott Whitehead has been discreditied by those who worked with him. In a nutshell they said he was a disgruntled FORMER employee. But once again it's all internet stuff so take it for what it's worth.
The last new Ford vehicle I owned prior to the 2008 Mustang was a 2000 Ranger and it called for 5w-30.
In the end you can believe what you want, it's a free country. I don't buy into the big conspiricy theory that generates lots of money for boutique oils and testing companies. All I need for proof is the excellent longevity reputation Ford motors have. Ford is always on the leading edge for motor technology as is Honda. Both have motors that last along time when cared for as directed. Both spec 5w-20 for most of their motors. I trust those results and their engineering team far more than I do random postings on the internet.
Sorry guys, the empirical testing just isn't there. Or should I say that internet rumors aren't enough to sway me and I will always question things that don't make sense to me. This is a prime example. More mpg would be the result of less friction. Worse mpg would be the result of more friction. More friction would cause more wear. The cafe theory just doesn't stand up to this very basic reasoning.
Still waiting on your answer as to why Ford specs both 5w20 and 5w50 for the Coyote engine
Same engine, same internals, nothing special, other than a different suspension package and an oil cooler.
Now the roadrunner variant of the coyote 5.0 calls for 5w50.
Your one answer was intended use, well if I intend to beat the snot out of my non track pack 5.0 that has the same engine as the track pack 5.0, then I guess using 5w30, 5w40 or 5w50 would be perfectly fine then.
What people don't understand is, not every oil is created equally. I've seen the tests on motorcraft 5w50. After just a few miles it breaks down and becomes a heavy 5w40, so why not just run a good grade 10w40? Hmm, that's what all of the GT500 guys do.
When adding cooler fuels like E85 or running cooler thermostats, you see plenty of gt500 guys switching to 10w30.
Ford's #1 concern is gas mileage. If they do not meet a standard they will be subject to heavy fines. 5w20 oil helps with this on the performance vehicles. Heck it helps on a lot of vehicles, but motorcraft 5w20 does not hold up well to sustained abuse. Paying out a few engine warranty replacements for rattles, slaps and knocks is a lot cheaper than government fines.
Most analysis I've seen on Motorcraft 5w20 shows that it is actually on the heavier side and closer to 5w30, so no harm in running a 5w30 especially if you are introducing more than the average amount of heat into the motor.
As far as people jumping and saying "well, that's what Ford spec'd for the engine" have obviously not worked in any type of product development/engineering life cycle.
The Engineer designs the specifications, Accounting runs it through purchasing to see what the units can be acquired for, if it does not fit a certain pricing model, it is rejected and the specification has to be loosened.
Don't kid yourselves, Ford did not contract Conoco to formulate Motorcraft 5w20 oils because they were top notch quality, they did it because they met their pricing model of Cost vs. Quality vs. Speed of Product Delivery.
If people wanted to follow the above logic "because the Ford said so", then I guess those stock mufflers are really the best... the stock suspension is the best for the car... the stock tires are also the best. No need for a supercharger, the factory Ford induction system is the best, also those headers... nah, the factory Ford stuff is the best.