Mercedes-Benz W203: engine does not warm up and the thermostat
Mercedes-Benz W203: why does the engine not warm up in winter?
The most common cause is a faulty thermostat: if it opens too early, the temperature stays low, and if it sticks closed, the engine overheats. Normal operating temperature is about 85-95 degrees. If the temperature does not rise above 80 degrees even on a longer drive, the thermostat is worth replacing.
Mercedes-Benz W203 CDI: what is the small auxiliary thermostat?
Some CDI engines have, in addition to the main thermostat, a small auxiliary thermostat in the upper coolant hose line at the front. If the temperature does not rise, replacing only the main thermostat is not always enough. The part number is A 0052033975. The 180 Kompressor has only one thermostat.
Mercedes-Benz W203: what else can be wrong if the temperature does not rise?
The water pump vanes may have come loose, in which case the coolant does not circulate. An air pocket in the cooling system can also prevent circulation. On a diesel, extra heat also comes from the electric element on the side of the engine, whose fuse or element may be broken. A clogged heater core leaves the heater lukewarm.