Mine sits for many days at a time and never a problem up in North Dakota. The worst time was about 8 days without running, pointing front first into the cold north winds, air temp -20 to -30F with windchill running -50 to -55F. Unbelievably cold but she started up first crank. I should have plugged it in but it was too cold to mess with and I wanted to see how it started. It was loud and didn't like it but after 30 sec it idled up and was just fine. This is on a 2012 LML, I use optilube as well so the fuel doesnt freeze up.
Plug it in if you want it to warm up quicker otherwise dont worry about it, it will start. Doesn't get much worse than what mine has went through.
We'd chill doesn't affect vehicles the same as people. It will cool them off quicker after shut down but if it's - 20 with a windchill of - 30 it's still only - 20 to your truck. I had to start mine in - 30 Celsius once after not plugging it in, started but didn't like it.
This is funny because my 2007.5 lmm started for a week an a half last year in steam boat colorado snowboarding it got down to -10 to -20 every night never plugged the truck in and fired like a kitten every night !! dont worry about starting a duramax in the cold.
Bills custom intake, mbrp duels, efi 5dsp, 3'' down pipe, fass 150, amp steps, 4'' fab tech lift , 22x12, 35' toyos, Front e-locker.
Simply put its so much easier on the engine to have it plugged in. Duramaxs will start when it's in the negatives, it will take longer to crank and you'll get a rough idle but it will start. Its just not good for your motor. Plug it in... you have a block heater, use it. Last year I had to cold start all winter because I had nowhere to plug it in, and it fired up every single time. Coldest it got was 0'f and it fired up after cranking for 3-4 seconds. Regular conventional oil and some diesel Kleen.