Give us a few details as to the conditions when it is overheating (outside temperature, operating speed, grade, etc). The thermostat should open about 180 degrees. In hot weather, on uphill grades 200 is not unusual. In cool weather, on level roads, you should be running 180-185. If you are running 200 in cool weather on level roads, you have a problem that needs to be addressed. Either a stuck thermostat, a plugged radiator, a very dirty radiator, low coolant, or a faulty dash temperature gauge, or multiples of these. If you have a DDEC readout, go by it rather than the dash temperature gauge. If the transmission temperature is running 200 other than very hot days up steep inclines something is definitely amiss, although 200 degrees will not harm the engine or the transmission (200 is the top of the normal operating range for the HT 740).
Additional information, including the last time the radiator was steam washed would be helpful.
Now as to your question about radiator misters, in hot weather they can and do work on grades. The easiest way to get the water is from your fresh water tank BUT it will have minerals in it that will form scale on the radiator fins so it is best to use a separate tank with its own pump and run distilled water. You will need a tank that holds several gallons of water, a water pump, tubing from the tank to the pump to the radiator, metal lines that can be run inside the fan shroud and spray heads to mist the water over the inside of the radiator. Run a wire to the instrument panel (if you have any extra wires from the front panel to the rear electrical panel in the engine compartment you are in luck) to use when the temperature hits about 195.
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