weird coolant warning

Hi can anyone help, My 2000 c200 kompressor is giving a "coolant visit workshop" warning when I start up from cold, it does not happen when warm. the woefully poor manual indicates a fan problem, however I waited until the car reached just above nominal temp and the fan kicks in and the temperature drops, no overheating at all. I checked coolant level and its full with no leaks. I am puzzled, I phoned mercedes direct and they stated " thats a strange one" they told me to book it in to the nearest dealer but if they have no clue it could be very costly :confused: