you never want to remove the thermostat, most on them on mercedes have a dual function, if you remove it coolant will not be properly diverted, not only does the top part of a thermostat open but when the top is open the bottom closes off (see picture) with it removed coolant will not enter the radiator as it should, most of it will circulate from the block to the cylinder head,not really making it to the radiator to cool properly.