In the 78° ambient temp it seems the ECT wants to settle around 174° as long as the car is moving at 50+ mph, which is a few degrees cooler than a 4.6L DOHC setup. Short WOT bursts resulted in no more than a 2° rise in ECT. Thermostat seems to flow to rad pretty well by 182° and the stock GT500 fan/radiator setup proved more than adequate, easily controlling temps with the low speed fan. I think this is testament that the GT500 cooling system is pretty well done. It's hot-side thermostat housing design is superior to the 4.6L DOHC and favors high flow to the radiator, maximizing the larger diaphragm t-stat, with the coolant forced to take a 180° turn around to go back into the bypass. I feel confident that the 182° low fan setting will keep ECT in a target range of 176-184° under most city driving conditions.