cooling system

[I have arrived]

I have a 94' S350D and would like to know what the normal operating temp. range is.

There is a mark on the gage for 80C then above that an unmarked dash and the next mark at the upper extreme is the point of no return 120C. Where is the safe zone?

Also for this year & type of engine, is there 'special' MB coolant I should be using or is 50/50 diluted Prestone usable? I'm not sure if the aluminum head requires anything special or if the radiator might react with regular coolant.

Thanks