From swinging the key to start the ignition.The overheating light will go on and the fan will work extra hard.The light stays on until i am driving for a couple of minutes.Then i will have to switch the car off the switch it on again when the needle on the heat gauge moves the light outomatically goes off.What could the possible problems be, i was advised that i should change the reservoir , would that be correct .

Please help ...Desperate .