Motorcraft 10W30, 5W40, Rotella or Mobil 1 for 6.7

I use whatever Costco has on sale....usually Rotella at less than $4.00/qt.

Book calls for 5W-40 synth, put in 5w-40 synth. 10w-30 is to thick for the 6.7L in my thoughts unless it's really hot. 5w-40 has really improved the performance/starting of my 6.0PSD

As for the flavour I put in what ever is on sale. Truck does not seem to care what brand.

I always go by the book. I am not a huge fan of most dealer advice and suspect that the party covering the warrentee is more important to please. On that subject, I have never seen a factory recommendation for high mileage oil at an extra dollar or two per quart.

As long as the spec listed in your owners manual matches the list on the oil container you are good with any of them.
I really question a Ford dealer that ignores the factory requirement for a particular weight.
They are documenting their error on your receipt aren't they?

Rotella T6 5-40 Synthetic is all I've ever used. Ford is on a band wagon tho when it does to fuel treatments......but that's another story.

I would go with the 5W40. The early 6.7L Powerstrokes had very tight bearing clearances(3/4 the size of a human hair) and were known to spin bearings in colder climates using heavier oils like 15w40 or 10w30. Also, due to oil routing design, it takes a lot longer for the thicker cold temp oils grades to get to many upper parts of the engine.

There are extenuating factors with todays engines that nobody thought of before. You can use a wrong oil for some time before issues arise but eventually, they will bite you. Hard.
No way would I use anything but what Ford recommends.

As for the Mobil One vs the Rotella T6 I would go with the T6 since it's on Fords approved oil list.

As for my truck I run Motorcraft 10W30 year round and purchase it and the oil filter from Wal Mart.

My Cummins and my Ford have integral oil coolers so I imagine when the engine is at operating temp the oil is running at or near the same temp whether winter or summer. I use the mfg recommended oil spec for proper lubrication on start up.

"Book calls for 5W40 (full synthetic)...Local Ford dealer uses 10W30 as standard oil change oil."

Interesting a Ford dealer has decided that Ford doesn't know what is best for its engines.