I agree with Bo, about the "squeezing" 1 mpg out of the engine. The big push for 5W-30 is for fuel economy only. To the normal person, what's 1 mpg better fuel economy. However you multiply the 1 mpg times the number of cars GM builds, it adds up. Many owner's manuals even list 5W-30 as only good for up to 60 f. only. My father-in-laws '93 Subaru says not to use 5W-30 for temps above 20 degs. Personally, I'll take superior long term protection over fuel economy.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member