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

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2000 C230 Kompressor "Frosty"

2007 PT Cruiser
2001 VW TDI Beetle
1999 Landrover Discovery II
1971 Corvette

Gone: 97 Cabrio, 83 240D, 93 VW Eurovan, 95 Volvo 850, 93 Chevy Astro Van, 77 VW Bus, 99 VW Jetta, 74 VW Bus