Date registered: May 2016
Vehicle: 2000 S430, 2003 S430, 2003 S600 TT, and 2005 E320 CDI
Mentioned: 169 Post(s)
Quoted: 962 Post(s)
No need to switch back if you don't want to. Since I live in an area where it does get below freezing in the winter, I've taken to using 0W-30 even in the Honda Civics (the book calls for 5W-30 or 10W-30). This is because of what Dave pointed out, above, about the "W" rating for oils. In my Benzes, I continue to use 0W-40 (Mobil FS European Formula). Works great. In Las Vegas or Phoenix, AZ summers, I think 5W-40 or even 10W-40 would also work, due to the ambient temperature.
When it's cold, I *want* lower viscosity, and all it means is that shearing of the oil molecules will take place a little sooner, vs. if the W rating and the "hot" rating are closer. That's all. However, remember that M-B's computer says to change your oil typically every 10,000 miles (the "A Service"). I do it every 5,000 miles. This seems to work well, because the '03 S430's engine has gradually quieted down over the last couple of years. And in all of my M113-equipped cars, I use exclusively the white "fleece" filters, instead of the paper ones (the S600 and the E320 CDI factory filters are paper, so they're different).
So, you're fine.
2000 S430 (Dad's car, used for special occasions)
2000 S500 (wife's DD: my first W220 project car)
2003 S600 ("sex on wheels"--second w220 project car)
2003 S430 (one of two current DD's--third W220 project car)
2005 E320 CDI (the other current DD--first W211 project car)