Ali is absolutely correct.

I think at www.mbklasse.com under the username "9KRPM' I posted some nfo on doing a C240 coolant change.

When I did my coolant change on my rwd C240 I couldn't get to the engine drain plugs, though you may have better luck than me.

I ran the heater on high and left those settings when I flushed ( engine off ) and when I purged air bubbles ( engine runnning ).

The radiator drains easily enough, and the refill took one container of MB coolant plus one gallon of distilled water, I mixed both together beforehand.

Ran the engine with the pressure cap off for over five minuted to purge any air bubbles after the refill.

My factory fill was dark blue, then with the added regular yellow color MB coolant my resultant fluid was blueish/green.

You know how to remove the plastic engine cover?