Okay, I've read a thousand responses about the diesel engines running hot, but I'm still confused. I have an '86 300SDL that reaches close to the 120c (red mark) in hot weather with the a/c on, in stop & go traffic. It will lower when I start moving again. The Mercedes dealer says it should reach that high and I need a new radiator. Another Mercedes expert says I don't need a new radiator. My auxillary fan is working.

HOWEVER, the owners manual states "During severe operating conditions and stop-and-go city traffic, the coolant temperature may rise close to the red marking".

Is my car normal when running hot in city traffic?