Observe safety regulations for engine cooling system cap - AH20.00-U-1000-01Z
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2011 Mercedes-Benz ML350, 2010 Mercedes-Benz ML350, 2009 Mercedes-Benz ML320, 2009 Mercedes-Benz GL320, and 2008 Mercedes-Benz ML320. However, it is still accessible from the selected car via links, so may be relevant.
Open expansion tank/radiator cap only at coolant temperatures below 90°C
Danger of scalding