A couple of factors are in play here. A thermostat sets the MINIMUM temperature a cooling system sees by restricting coolant flow until its opening point is reached. It's up to the radiator, the fan, and the water pump to maintain that temperature once the thermostat opens and coolant starts circulating. Idling is a poor way to evaluate cooling system performance- - - -neither the water pump nor the fan is turning fast enough to be efficient. Install whatever temperature thermostat cranks your tractor- - - -I prefer a 180, and set the engine speed up to around 1500 RPM with the idle speed screw to see where the coolant temperature stabilizes, or do it the right way and take a test drive. I'd recommend using a laser thermometer to check various places on the engine block, hoses, and radiator core to see what's actually happening- - - -a dash-mounted temperature gauge is a wild guess at best.
If the coolant isn't boiling, the engine is not overheating.
Jerry
