[landrovered]

Driving long periods heats up all of the parts of the car (saturated heat sink) which requires a longer cool down than simply driving normally day to day. After four hours of driving it could take as much as six hours for the entire car to reach ambient temperature again. In normal conditions it should cool in two hours depending on ambient temperatures.

I am referring to the metal parts of the car. The temperature of the coolant is dependent on the total volume of the cooling system and the amount of surface area for heat to be exchanged across.