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.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section