Did you get the air burped out of the system after the thermostat replacement. I may be getting my models mixed up, but I'm pretty sure that there is a bleed screw on the thermostat housing on your car. It is used when filling coolant WHILE ENGINE IS COLD!

Not all thermostat housings have this bleed screw. The other way to bleed is to loosen the bolt on the head closest to the front of the engine just over the first injector.

In the image below you can see the bleed screw on top of the thermostat. If you don't have this you can see the referenced bolt in the background near the injector

believe it or not you want the engine to run hotter since it will perform better. Engineers specified that thermostat for a reason. The hotter the engine runs the most efficent in terms of combustion and fuel economy.

my 190E gets around 100c when its really hot out when im sitting at a light but on average day it runs steady at 90C when im crusin

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Remember that you have to get the oil temperature above 212F (100C) to cook off any condensation. If not, you make sulphuric acid. Not a good thing. So the closer you run at 100C, the better.
Anziani
'93 300CE 175K
'95 E420 117K

No I did not bleed the system. Maybe this is the problem then? Do I need to drain the coolant again or just pop that bolt?

I don't have a plug on the thermostat housing.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k