Mercedes GLE Diesel Engine Overheating

I understand your concern regarding the engine overheating and extended warm-up time in your Mercedes GLE. I experienced a similar issue with my old BMW 3 Series, although it was a petrol engine. The symptoms you described strongly suggest a malfunctioning thermostat. It's responsible for temperature control in the cooling system. Did you happen to notice if the radiator fan is running excessively, even when the engine is cold? Also, have you checked the coolant level in the expansion tank? If it's significantly lower than usual, it could indicate a coolant leak, even if you haven't spotted any visible puddles.

Thanks for the quick reply! The radiator fan does seem to be running more than usual, even when the engine hasn't fully warmed up. Coolant level seems okay though, maybe a tiny bit lower, but nothing major. Is there any way to confirm it's definitely the thermostat before I spend money on repairs?

Given that the radiator fan is running excessively and the engine is overheating coupled with a slow warm-up, it does reinforce the likelihood of a faulty thermostat. While a definitive diagnosis requires proper testing equipment, these symptoms point strongly in that direction. In my experience, attempting DIY repairs on modern vehicles can sometimes create further complications. Considering the potential for further damage and the complexity of the cooling system, I would highly recommend consulting a qualified mechanic. A malfunctioning thermostat can lead to engine overheating, potentially causing severe and costly damage. I think it is the thermostat, and I'd get it checked out before it gets worse.

Okay, thanks a lot for your help! I appreciate you sharing your experience. I'll take it to my local workshop. They suspect it's the thermostat cooling circuit motor, and quoted around 350€ for the repair. Hopefully, that fixes the issue.