An update after the t-stat replacement.
Engine is running much cooler at 87 to 90 degrees, and the auxiliary fans kicked in on and off even the temperature is at around 90, and the high pressure could have triggered the fans before the coolant temperture get too high. In traffic, it rose slightly to 100, and not higher. It almost run as cool as before the water pump got replaced.
Thanks again for the advices.
1994 C280, Red hot with cream interior 106K miles
2000 ML 320 Silver
1991 190E 2.3