help please last night whilst going to the gym i noticed that my car took ages to start then i could constantly hear the coolant fan whizzing away. once i arrived i stopped and restarted the car and everything seemed fine. on my way home the fan was quiet until suddenly the temperature gauge shot up into the red within seconds it dropped to 40oc then back up to 80oc then into the red and it continues to do this. it has enough coolant in but i'm unsure if it's circulating properly around the system as if the pump is not working. does anyone have any ideas or knowledge of a common fault ?