Mercedes-Benz W210 cabin does not warm up or warms up slowly
Why does the W210 cabin not warm up properly?
There are several causes: the thermostat, a blocked heater core, weak or wrong-strength coolant, air in the cooling system or a faulty electric circulation pump. Blocked fresh-air filters also weaken the airflow.
Does replacing the thermostat help?
Often it helps, but not always. Besides the main thermostat the car may have a small thermostat, and both should be checked. If the temperature stays low even after the replacement, look into other causes. Covering the front of the car in cold weather raises the temperature.
Can the coolant or the heater core be the cause?
Yes. Coolant that is too weak or too strong can become thick in the cold, and then circulation does not work. The heater core freezes or blocks easily, and flushing it can help. Check the frost protection before winter and change the coolant if necessary.
How can I tell whether the circulation pump or a leak is the cause?
If the heater blows cold at idle but warms up when driving, the electric circulation pump is suspected. If the cooling system holds pressure and bubbles, the head gasket may be leaking and bringing air into the heater core. Have a workshop check it.