Yes you can leave it running all night.

The risks are:

- things going wrong that if attended would not be a disaster, but unattended... broken belt or hose, low on any of the vital fluids.

- in really cold weather, idle speed is not enough to keep the engine up to temp so you get more fuel by the rings into the crankcase, figure out a way to increase the idle speed and then change your oil at 1/2 your normal interval

- never do this on WVO for the reason stated above

__________________
Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO