If it won't crank/turn-over, the battery is the first problem. Charge or replace your battery. If it won't stay charged or won't charge from driving, you have electrical problems.

Fuel here in Michigan is fine at 0F, it has been well above that during the day also, so I doubt that is your problem.

Diesels fire from the heat of compression. The faster you crank, the more heat it produces and the more likely to start. Bad starter/battery/alternator/wiring can all contribute to slow cranking and that will often result in a no-start when it's cold.

Synthetic oil also helps in the winter as it allows the engine to crank more easily, and the block heater will help with heat and cranking speed.

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Gone to the dark side

- Jeff