Wait, is it struggling to cool at idle/slow speeds with the a/c running? With no a/c on, my car maintains 85°C with outside ambient temp at 105°F, no aux fans running and cruising at low speeds, 20 mph - 25 mph ± 5 mph. With A/c running and low speed fans on its the same thing. Try rechecking fan clutch and radiator fins.

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1990 190E 3.0L