I have a 1995 E320 Wagon, and need to flush the cooling system after the headgasket replacement. I opened both the drain plug at the bottom of the radiator and the drain plug at the passenger side of the engine blocked, and was only able to drain out 6 US quarts of coolant. The manual says the total capacity is 10 quart.
I notice there is a bronze plug bolted on a metal tube right on top of the engine block, and I am not sure whether there is AC fluid or coolant inside, do I need to release this one too?
Any thoughts? Thanks!

 

Remove the lower radiator hose itself as well as the radiator drain valve.

Also there is a return hose from the heater core, you need to get that one off.

You will never get all the coolant out of the block.

Make sure you only use genuine MB coolant when you refill, I always use distilled water instead of tap water.