Oil question

[WMO Madness]

I am sure this question has been asked many times, I am going to use the "newbie" excuse for asking it. As I was doing some cleaning in "Miss Doris" today I found several old oil change stickers on the doors jam, one was clear showing they used 10w-40 oil. I use 15w-40 Rottella in my Ram, is this weight too heavy for this Benz or the 10W-40 that was used previously by the mech who service this car?

[vstech]

back in the 80's and 90's, most motor oils had the C rating, today with environmentalists lobbying everybody, only a select few motor oils still have the C rating, so what ever oil you decide to use, it's got to have at least a C rating in the circle. CI or CJ most likely... crude based oils are less expensive, and they will be 15W40 Synthetics are a little better for the motor, especially in winter cranking speeds, and they will be 5W40. brands are important, but everybody has their own opinions on which one to choose. usually based on dollar per quart...