mine got to the mark after 80 degrees. is that 90 or 100?? the head I have had fixed and I have put in a new headgasket etc etc new bolts yes, turbo too. but I don't trust these 603's at all and I don't want it to break straight away...

I used to run my '86 citroen diesel with a bad radiator in spain (hot with mountains) up to 114 degrees. then the electronic display would start blinking and I would stop to let it cool off. did that 26 times on my way home to the north of France. the car still runs fine... aluminium head by the way, 2.5 turbo 5 speed. would go 195 km/h.
anyway, thus I am used to not worrying about engine temps but with mercedes it's a different story I've heard.