I have an 85 300SD and had some issues starting in a really cold weather in Chicago. Most people are aware of those chill factors in that area. So, I asked my long-time MB mechanic about that. He recommended that I put about 1 gallon of gas and then fill the rest of it with diesel. Gas has a tendency to 'dry out' all of the rubber hoses and other rubber components. To avoid that I poured about 1 quart of the ATF as it was recommended by my MB mechanic. Once I started doing it, I never had problems starting my car during Chicago winter.

I don't think I would pour hot water on the engine block or set a fire underneath the oil pan if other and safer alternatives seem to work. I agree with previous posts that you should check the compression, possibly do a valve adjustement, check to see if all glow plugs work properly, check the fuel filters and, on top of that, don't go to those cheap gas stations to get diesel. Go to reputable ones. Lastly, it is much easier to run on a synthetic oil than the organic one. Your engine will appreciate that during winter. Good luck.