Mercedes X Klasse Diesel engine overheating

I might be able to assist you. I have a Mercedes X Klasse as well. I experienced something similar not too long ago. The engine took ages to warm up, and occasionally the temperature gauge would creep towards the red. Did you notice if your cooling fan was running excessively, even when the engine wasn't particularly hot? Also, any signs of coolant loss? I'd be curious to know if you've checked the temperature sensor readings with an OBD2 scanner.

Thanks for the quick response! The cooling fan does seem to be running more than usual, even on shorter trips. I haven't noticed any coolant leaks, but I'll definitely keep a closer eye on that. Regarding the temperature sensor, is it easy enough to access? I have an OBD2 scanner, so pulling the data shouldn't be a problem.

Okay, the cooling fan running excessively is a key indicator in my opinion. Yes, the temperature sensor is relatively accessible; it's usually located near the thermostat housing. I still think you need to consider the thermostat and the water pump. While the temperature sensor data is valuable, my strong recommendation would be to have a workshop check the map thermostat. Based on your description and my experience with the same engine, it seems like the most probable cause.

Thanks again for the advice. I took it to my local mechanic, and you were spot on! It was indeed the map thermostat gone bad. Total cost including labor was just under 350€. The cooling system seems to be working fine now and the engine warms up much faster. Appreciate the help!