Now I don't know about other Mercedes engines, but my 617.950 diesel has the capability to bleed air itself. Per the service manual, the thermostat housing has a passage built into it to bleed air off and work it's way to the recovery tank. Got to love those engineers.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member