In reference to potential thermostat problems you should know that the T-30 2.5 L engine (QR25DE) actually has two thermostats, although Nissan refers to one as a "thermostat" and the other as a "water control valve". The 'thermostat' is in the housing that the lower rad hose connects to, just behind the first catalytic converter unit. The OEM is a 180F (82C) unit. However, the 'water control valve', a critical component, is inside the 'water control valve housing' that is technically at the back to the engine, so at the right when you look in from the front. The upper rad hose connects to that housing, along with connections to the oil cooler, the cabin heater and the small heater in the electric throttle actuator. That valve/thermostat is a 203F (95C) unit. The service manual has a flow diagram that illustrates the various coolant flow patterns in the engine and it is a mind-boggling diagram. In the case of the original poster's issue if the 'water control valve' has failed and stuck shut that would lead to overheating, although that valve when closed does not block all coolant flow back to the radiator. However, the temperature sensor is positioned in the 'water control housing' such that it should give an indication of overheating, assuming obviously that part is functioning properly.