They are supposed to be self purging. When you refilled with water and engine running did you turn on the heat, drive around and top off?

If the radiator is old I would replace on principal. The last thing you want is overheating on a 603.

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42