Patman:
I would never consider a 5w-30 either.
Again, better oils bracket it on both ends.
If start up is a concern, a 0w-30 is what I would use (but not a MOBIL 30 as they spec out so thin).
Or maybe a MOBIL1 0w-40 (which I currently run and it outperforms a 5w-30 from same manufacurer on both ends of the spectrum).
There are many good 5w-40 available too w/ similiar start-up abilities to 5w-30's but better film strenght.
All the above is comparing weight of same manufacirers against each other.
As for "tighter clearances" in modern engine that just doesnt hold any wayter as clearances have more or less stayed the same for most applications.
Also Of course the same engines that in USA are often recommended 5w-30 or even xw-20 are recommended xw-40 in Germany, Australia and Japan.
If you go back to the 80's u will find that teh 2.8 L Inline 6 are recommended by temp range from 5w-30 (thick of northern winter) to 20w-50 (southern summer).
The last couple of years that (nearly ) exact same engine was offered in USA it was recommended 5w-30 year around!!!!!!!
Obviosuly the engine doesnt actually change magically as it crosses the Atlantic.
As for warranty voiding:
Its teh API service requirement that needs to be met bu an oil that you use aftermarket, I admit I ahvent read fords wording (could u scan it for us?) but all otehr manufacturers make recommendations based on viscosities, and dictates only with reagrds to the rating (such as SL for current model years).
If Ford takes it one step further I'd be interested to see it.
Also in recent years the first few unusual engine failures in hi performance engines have cropped up (not just in M3) and low and behold all those engines used to have 40 or higher recommended and now recommend 30 weights.
there is esoecially need now than in previous yeras to got o thin oils because we now have acces to 40 weight oils that flow better than outright winter oils of 20 years ago.
My old (83) Saab Manual btw says: Do not run a winter oil such as a 20 weight oil at extended hiway speeds even in winter.
In those days they recommended 40 +50 weight in summer, or 40 weights in mild climates year around (10w-30 were "acceptable" as well).
And now low and behold the last few years of production of that engien recommended 5w-30 yera round with no significant change in the engine.
Hence the "we recommend thinner oils cuz newer engines are tighter" arguement manufacturers field is simple disinformation.
Fred...
