W221 the coolent water coming out from the water reservoir and the engine now running?

 

is this coming after some car servicing / work on the cooling systems? if so might have been overfilled

if no work undertaken, is their any other indication the car is very hot - engine temp gauge, funny smells, sluggish performance, engine stalling around idle ? if so turn it off wait 2 hours then check things out

which engine - what mileage, is their any coolant in the car (don't ever open rad cap on a hot car (its dangerous)

the likely unfortunate issue with be terminal overheating and very large costs - servicing / preventive maintenance as a car ages is a necessary part of life