Q: Temperature gauge problem on a 2005 Mercedes Benz S500

Hello - I would first check for problem codes, whether the Check Engine light is illuminated or not. And, if the engine is not really overheating, the problem is most likely the engine temperature sensor (the sensor for the gauge, not the sensor that feeds engine management - they are different), or the wiring to that sensor. A very high temperature reading would suggest that the sensor or it’s wiring is shorted. I recommend a engine overheating inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, confirm this diagnosis, and give you an accurate assessment of damage and cost estimate for repairs.