I have an 02' duramax and have let it run so far today because of the temps being -15 below and all.

I guess my question is because I don't have a idle up switch on there is letting sit there and idle as long as I have in the cold temps hurting anything at all?

the only real concern I can think of would be cylinder washdown from fuel that didn't burn.

-15 today here as well, truck not plugged in and it still started, however it took two cycles of the glow plugs to get her going.

I had mine plugged in fired up perfectly and have a 50/50 blend so all thats good just worried about wrecking something by letting it sit in the parking lot idling for most of the day at work is all.