140 s280 overheats when in traffic or still

I have well was represented to be a 97 s280 more like a 95 it's still in court. the temperature on the highway runs and around 90 when stopped at a traffic light or even to get gas or pay a toll the temperature suddenly increases to 100 plus when it gets to around 110the car will stall and not start until it is cooled down.

I have taken into the Mercedes dealer we have replaced the radiator and many others. Cap valves.but the problem persists. When we take off a cap with electric wires it allows the fan to spin full speed all the timevery noisy however after this cap is removed the temperature goes down right away. There seems to be 4 wires going into this plug. Any ideas.your help would be most appreciated thanks again. MI