I appreciate your comments since you have already tried 0W40 in an older MB. I had not considered the possibility of an engine "rattle" upon start-up but I am sure the greater tolerances of an older MB (due to both initial tolerances and wear) have something that contributes to that occurrence.

The only reason I was considering using 0W40 was that the oil packaging indicates that it conformed to MB specs whereas 15W50 has no such claim. The packaging also indicates that 0W40 conforms to MB spec number (?) and the 15W50 conforms to a different European spec number. Granted, the 15W50 may be what is required for older MB's and the new MB spec is what is needed for newer higher tolerance engines. I am sure that either would be safe to use since 15W50 is even recommended for my 2000 ML320.

So far 15W50 has been fine and, since it is Mobil 1 synthetic, I would not think it would any problem to use even when it gets down to 0 F in the mountains of NC.

At least Mercedes is still recommending use of viscosties that have a high viscosity rating above 30, not like some manufacturers who are now using 5W20. 5W20 really makes me nervous when driving down the highway at 70 mph when it gets over 100 F in NC.