W140 s500 coupe, has begun to overheat. Normally it temps at approx 80-90 but now goes into 110+. I believe the thermostat operates at approx 80 c, vicous fan at approx 100 c and aux fans beyond that. Both aux fans are operating. I have replaced rad cap as it looked worn but problem is still there. Considering the car previously never reached 100 i'm suspecting the thermostat. Advice required before i cook the engine!