Originally Posted by Stretch

The point of the original Mercedes system is partly to protect the plugs - there's a chance you'll burn them out if you start using them for long than intended.

If you are having a rough time getting the engine started have a look at the condition of the engine oil (fresh oil always helps), the health of the starter (a rebuilt starter spins faster) and if necessary consider fitting a block heater.

I feel compelled to add that In most (weather) situations in the Netherlands I've never had trouble starting my OM617 (or any other vehicle)