If your car won't start, it's not because the oil is to thick,, at this point, you have other issues. I would suspect lack of fuel due to a clogged filter. But could be something totally different. How long since the valves have been adjusted? Are all your glow plugs operating?
It's hard enough to start a Mercedes on 80-90% WVO (10-20% diesel) first time every morning. It's near impossible to start if a few glow plugs are burned out.

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