Diesel MB engines need several things for good cold-weather starting:

1. the right fuel for the season
2. working glow-plug system
3. a GOOD battery (usually no more than 3 years old)
4. good compression (e.g., by regular valve adjustments)
5. fast-enough cranking.


#5 above is related to the health of the battery, but also to the viscosity of the oil. It's been shown (don't have my finger on the reference right this instant but have seen it with my own eyes) that synthetic oil SIGNIFCANTLY improves cold cranking speed, and thus should help with building enough compression heat to start in cold weather.

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Steve
'93 400E