The viscous clutch fan on these cars is marginal in this type of weather. You absolutely need to the aux fans on in order to keep the engine cool while sitting in traffic at 100f. Do the "cool harness" modification to keep the aux fans running in this weather.
http://www.benzworld.org/forums/w124-e-ce-d-td-class/1629476-auxillary-fan-turn-set-point-resistor.html

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CENSORED due to not family friendly words