coolant change C230K, M111 engine
 

Does draining the radiator also drain the "fill tank with the cap on the passenger fender-well"? To refill, just pour coolant into this tank until it fills the radiator and this tank. It appears that there are electrically controlled valves in the coolant lines between these two pieces? In my other cars I would call this fender tank the overflow but in this case is it part of the radiator, as far as filling and draining are concerned?

Yes, draining the radiator will drain the overflow tank. The two electric valves are for the heater. You also need to open the block drain plug, it's on the passenger side at the back, near the O2 sensor in the exhaust. I would also use the citric acid to flush with, then drain and fill several times to clean it out, then fill with mercedes coolant (or Zerex G05) and distilled water. Good luck, Chuck

Not sure about the procedures on the newer cars, but the citric acid flush was only to be done after a deoiling was done whether there was evidence of oil in cooling system or not. IMO neither is needed if the coolant has been changed regularly and comes out nice and clean.