Murano Diesel Engine Overheating

Overheating is never good. First thing, have you checked the coolant level? And is the fan spinning freely? It could be a faulty fan clutch if it's not spinning as fast as it should when the engine gets hot. Also, does the temperature gauge climb rapidly, or does it happen gradually? That might give us a clue.

Coolant level is fine, and the fan spins, but not like it used to. The temperature climbs gradually. I'm not very familiar with the electric fan system in detail. Could it be the electric motor, or some sort of sensor?

Gradual overheating with a fan that's not spinning properly definitely points to a problem with the electric fan circuit itself. Could be a bad connection – cable or plug – preventing it from getting full power. Honestly, with those symptoms, and not wanting to risk further damage, I'd take it to a workshop to get it checked out properly. They can diagnose the electrical system and fan motor.

Thanks for the advice. I took it to the shop, and you were spot on. Turned out to be a defective plug connection to the electric fan. Repair cost 95€. Runs fine again.