Date registered: Jul 2006
Vehicle: 1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
Location: NW Arkansas, La Jolla CA, Hong Kong
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Om operating tempuratures in Dubai, please note its hard to find the correct MB coolant, and most shops use hose water, some even use "phony" distilled water which is hose water in gallon plastic jugs, and Dubai hose water even with correct coolant causes corrosion problems. That's why corrosion causes so many thermostat replacements and radiator replacements are commonplace in Dubai.
On the aux fans, even correct aux fan operation will not overcome a partially corroded Dubai radiator core.
If your cats were bad, you would feel it all the time, not just at higher engine temps.
If it was me, I would pull the thermostat as visual check for corrosion in the system, if it looks corroded then assume you have a partial blockage of the radiator (actually a new thermostat and new radiator is "not so bad" price in Dubai), flush the cooling system, replace with correct MB coolant or Vavoline Xerez G-05 and your own store bought sealed distilled water, and add either Redline Water Wetter or Royal Purple Purple Ice coolant additive.
Aux fans primarily are to add air flow over the aircon condensor to help push that heat thru the radiator better, but nothing overcomes a Dubai partially clogged radiator really.