No thermostat means it would run cooler
SORRY, not in a Mercedes. The thermostat has TWO plates, main coolant circuit is closed when cold by one plate, the secondary(or bypass)circuit is open, forcing ALL coolant to flow thru block and head. When the main circuit opens as the engine warms up, the bypass progressively closes, forcing ALL coolant thru the radiator.If there is no thermostat, or a slightly leaking one, there will be reduced flow thru rad and higher engine temps.
I concur with psfred, check the simple stuff first.
You do not describe the operating conditions that bring about the *high temp* nor the body type, year or engine (M111 or M102 or....)
If you have the temp rising in stop start traffic, checking or changing the visco fan clutch may be the answer. Check with the parts suppliers for the *tropical fan clutch* that Sachs supply.
If it keeps rising when screaming along at 160kmh, you need a bigger capacity radiator, either more tubes per inch(denser) OR the biggest assembly that will fit in the space
Do not waste your time and money on an oil cooler.
Been there, done that
