Just found this:

...Coolant is a 50-50 mixture of purified (not tap and not distilled) water and antifreeze/coolant. Do not add straight water if the reservoir is completely empty as this can cause your car to overheat.


Source:
http://www.***************/mercedes-auto-parts/mercedes-auto-maintenance.html

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz