Chosen Solution
My Mercedes-Benz cooling system temperature decrease when I drive for a long time, nevertheless there is a thermostat in the system. The temperature is between 50 and 80 celisiou but it should be stable at 80. Are there any reasons for that
Coolant thermostat failure or perhaps someone has removed it. It is easy to remove and observe thermostat behavior in a pan of heated water on a cooking surface. These devices can come apart eventually due to corrosion and normal wear.
@mohammedmerc check your temperature sensor to the gauge to make sure that your temperature truly decreases with longer drives. We would need to know the exact year and model of your MB to try and help you further.
