Think about this for a moment. The role of the thermostat is to force the engine to operate at a minimum temperature, i.e. the degree setting on the thermostat. It opens when that temp is reached. Now, whether it's beginning to open or all the way open is irrelative, because everything that happens from this point on, lock up of fan dampers, startup of aux fans etc. is for the purpose of lowering the coolant temp down to where the thermostat closes. Then the process repeats. If you're thermo is open all the time, then your cooling system is inadequate either by design or malfunction. A good cooling system, be it on a Mercedes or an earthmover should keep the engine near the thermostat setting whether it is at idle or under load. If a manufacturer wanted the engine at 100C, they would put a 100c thermo in it.