Your glow system and battery needs to be in tip top shape. 12.7V is fully charged battery. Put a volt meter across the battery terminals when you crank. It should drop a volt or so but not more. Print the dieselgiant glow plug diagnostic page. You can easily troubleshoot most glow system problems - even in the cold. When was the last time you changed filters?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.