Originally Posted By: akela
Originally Posted By: demarpaint
Originally Posted By: akela
Engineers have a habit of designing for the "worst cases".
For automotive engines, the worst case would be: wide throttle, high RPM for the extended period of time. I am quite sure that Xw20 is noticeably underperforming in such conditions (although it may work fine under all other use cases).
When they were specing 5W20 weren't they designing for the worst cases? I heard that here many times before, about all the testing under the worst conditions. Like towing across the desert in 100F+ temps, etc. The more I think about it the more I think they had problems, and aren't about to share it with the car buying public. Now the question is will some of the other mfgs. making trucks that might actually see HD use follow suit? Time will tell.
Of course they've tested it under severe conditions; but the question is, what was the result? It may greatly vary from "barely acceptable" to "excellent".
And, yes, engineers often work under pressure from the management side to re-prioritize the criteria. Like, fuel economy over reliability/longevity.
I truly believe they tested it, and agree with what you said. Maybe now they realized they could have better results, and less problems with a 30 grade oil. Something sparked the change.
IIRC the word "adequate, ample", and a few other choice words were used when 5W20 was mentioned in testing. I mentioned it in some threads took a bit of heat for it. Those were words that never left me feeling warm and fuzzy. I was all for 5W20 when I bought my 08 Liberty and following mfg specs etc. But to be honest I was never comfortable with the one size fits all mentality of my 08 Liberty owners manual when it came to the oil choice, 5W20 PERIOD in any and all conditions. Especially when prior years used 5W30, and nothing changed with the engine internals. Then I learned about CAFE credits etc. a while ago and now decided next time I change my oil in it I'm moving to a 30 grade. The .0001 mpg I'll lose I can live with.
As I said earlier, it will be interesting to see what other auto makers say. The Pentastar engine started life running on 5W30, then they changed over to 5W20 only. Now you can use either 5W20 or 5W30 in it. The flip flop is interesting..
We all know that 20 grade isn't going to destroy engines, that's not what I'm saying. I just find Ford's change of heart interesting, and enlightening.