Not sure if this will work on the 190 but on my Trooper when ever I have had coolant out of the system I run it for a while with no thermostat in it at all and that helps flush out the air. I also will park it nose up while running it (on ramps on a slight up hill). The Trooper is known for air pockets in the head, a contributor to the fact that the early Trooper heads only last about 40,000 miles. (not quite up to MB standards!) Might give it a try.

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Currently
1991 Mazda Miata 174000
1991 Subaru 189,000 Winter beater

got rid of:
1984 VW Vanagon 195,000
1976 350SE Euro 185,000 KM
1973 280SE 4.5 (boy do I regret that)
1980 280SE European W126 4 speed manual (miss it)
1989 BMW 735iL 119000 (good riddance)