I'm in Raleigh also, and last winter I had no trouble starting my old 300SD that I sold. And it was being started with a blend of used vegetable oil and diesel. I rarely used the block heater, it didn't seem to make much of a difference. Just make sure your glowplugs are good. And don't just top off with MB coolant, make sure to flush all the old out every now and then!

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87 300D - Running on Veggie oil; 260,000 plus miles; Original #14 head