That's all it is, the car companies are helping themselves out, not you. At last year's Philadelphia car show, I saw a V8 Ford Crown Victoria and it called for 5W-20. Why not just pour in WD-40. Personally I will take engine protection over MPG. Here is the BIG sign that these thin oils have no real protection. Read the label on a bottle of any 10W-40 or thicker oil, you will see the words maximum engine protection. You will not find these words on the watered down oils. For your car, I would use 10W-30 or thicker. Look at the owner's and see what the thickest oil can be used for the current outside temps.

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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