Well now I'm thinking this engine has some kind of fuel issue. My BIL went to start it yesterday, it was cold, it wouldn't start. He checked the fuel tank and stuck the yard stick in the tank and swished it around trying to see if he could see something. Didn't see anything but went to start it and it fired right up. Then this morning it also fired right up at 30*. Go figure... Maybe I can just return all the grid heater stuff? Anyway I'm going to do a fuel filter and take a good hard look in the tank and the tank pickup.
hope its not the problem a friend found years ago on a customers tractor . . . tank was half full of dirt must of pissed someone off real bad . got lucky and cleaned it all out flushed lines and changed the filter 2x and good to go .
Could be moisture in the fuel, Your on the right track with changing filters. wouldn't recommend smaller micron in winter. All #2 diesel is treated after November in this part of the country, I use Stanadyne fuel treatment and mix little #1. Might not be bad idea to change the transfer pump, It's simple preventive maintenance, about $62. If it's starving the main pump that's about $1000. Cummins B series have been known to start without heater and Aid as low 0°. If it turns over and getting fuel it'll start, it was obviously getting fuel when you cracked the line open but maybe the pressure wasn't high enough for a good pattern out of the injectors. I'd keep the glow screen.