"The reason is that the older MB tolerances were designed for thicker oil"
This is BS plain and simple. Synthetic oils are not "thicker" or "thinner" than dino oils of the same SAE rating. They comply with the rating they have been issued. A synthetic 5w-40 flows better than a dino 15w-40 because of the "5" rating. It also performs as well as the dino does at high temps thus the "40" rating. The advantage is greater temperature flexibility. Synthetic simply works better for extreme temperatures. Believing that running the "recommended" oil for your car, even though the oil recommendation was written 20years ago, is the right thing to do is a stupid. Why not take advantage of the advances in technology? At least run a heavy-duty diesel rated oil. Why run oil that is intended for gassers yet meets 20yr old diesel standards? The good diesel dino oil costs the same. Its a cost/benefit relationship for synthetic. At $20+/gallon for Delvac1 this ain't for me. I'm not leaving ANY oil in my MB past the 4K mark as old indirect injection diesels simply put too much soot in the oil. My choice is Delo 5w-40 synthetic, $14/gallon its hard to beat for winter use. RT

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84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K