[PAUL SS]

An engine will continue to heat up after it is turned off due to lack of air flow because the car is standing still. Heat soak from the exhaust manifolds, heads and block will raise the coolant temperature eapecially with the thermostat closed. Any car with a mechanical water tempurature gauge will prove this.
So the temputature rises, opens the thermostat but there is no water pump running to move the coolant. Next best thing is for the cooling fans to come on to cool the coolant and it will naturally move (cold water sinks, hot rises.