Kyle,

I have used synthetic oils since the '70s when Mobil 1 first arrived and I was living in Alaska. Over the years I have tried other products, including RedLine and Castrol, as well as Mobil 1 in other than the original viscosity (15W-50 and 0W-40). While I believe the result was a more reliable cold starting experience, I could not verify it directly. Until recently when I switched the whole "fleet" (gas and Diesel) to Delvac 1. The 1982 240D has always been pretty reliable down to the mid '20s F. Below that it was not a sure thing and below zero it was pretty sure you would be push starting it. Well, on Delvac 1 the car has started on demand down to minus 10F. My daughter calls whenever the car fails to start or makes an unusual noise, and she has it in Troy, NY at college. She has only called once, and that was after a few weeks of really cold weather and a few consecutive days of trips of less than five miles each way which stressed the battery. Once it got back above 10F the car started on its own, no jump or anything. This is substantially better than it performed on any previous oil, including Mobil 1 0W-40. So, not to encourage an oil war, I think there are definite cold start benefits to synthetics in general, and these benefits are more pronounced with products specifically formulated for Diesels in particular.

Good luck, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)