Last winter, my first as a MB diesel owner, I didn't know I had a block heater already in the thing. To get through the winter (occasional -5 ~ -10F) i used one of those mega watt squarish type halogen lamps tucked up to the oil pan. Maybe not the safest thing to do, but the car always would start in the morning. On mornings like that I would let the engine idle for 10~30 mins before driving off. One, so it's be a little warm, Two, so it would at least be able to accelerate a little. I drive 90 miles a day for work and at speeds as high as 85 mph so carbon build up has never been a problem. This winter, after I discovered I had a block heater after all, I turn it on about an hour in the morning and the car starts right away. I still let it idle for the same reasons as mentioned above.