Start the car when engine is completely cold and remove the radiator cap. If you can see the coolant moving inside the radiator mouth, your car has NO thermostat valve. If so, get one installed (82 degrees should be fine). And about it getting cool on 5th gear, it depends on the speed and environment temperature. The wind hitting the radiator does the same job as both fans would do. On 5th gear the speed of car is quite high and temperature is not on the higher side these days in Islamabad so you might experience the same effect as if both fans are turned on blowing cold air on the radiator. I would also check for a faulty temperature sensor and low coolant / air in radiator. Sometimes air can get trapped inside and when an air bubble is on the temperature sensor nose, it will show the temperature as cold even though it is not in reality. And a bad temperature sensor itself can cause a whole lot of troubles in the long run, so check for these things and you should be good to go.