My 220D has a strong OM616 and I have started it down to minus 12. However, at that temperature it only ran for about 20 seconds and quit. Thereafter it wouldn't fire. I assume it gelled since I don't drive it in the winter and the fuel was purchased in the fall.

My 83 240D is pretty tired. Anything below 15 degrees is tough and below 10 degrees it isn't going to happen.

Both cars are maintained and in good tune. Both have good batteries and starters and neither has a block heater. Other than loop vs pencil glow plugs engine condition is the only difference and it makes for nearly a 30 degree spread on my two cars.

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1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K