Temperature Light Turns On


i have a nissan micra k12 year 2003 with 80k on the odometer.

i was driving on a moderate slope on saturday at around 60-70 km/r when suddenly the temperature symbol turns on (red). at the same time i noticed that the fan was revolving at the same time. i drove slowly afterwards and after driving 2 or 3 km further, the light went off. but the fan keep rolling.

i stopped the car and turn off the engine and let the car rest for around 15 mins. i drove slowly for around 10kms and the light and the fan came on again.

immediately i stopped and i opened the bonnet. i noticed that the coolant level in the tank was very high. it was near the cap. you could easily see the coolant when you remove the cap. car was rested for around 15 minutes again and i decided to return home. the light didn't came on but the fan was still on. i drove very slowly and rarely push the throttle. after 5 mins the fan went off and i kept driving slowly and sometimes dropped to neutral when going downhill.

on sunday morning i opened the bonnet again and the coolant level is no longer that high near the its cap. it has decreased and it seems to be normal again but still, it is above the maximum level.

there is no leakage in the radiator, the oil is still clear and clean, no smoke white or black and the car runs smoothly and it does not judder nor does the engine stalled. ignition is ok.

i also opened the radiator cap and i noticed a small amount of brownish paste, as if is a rusty paste. it is found both underneath the cap and around the inside of the hose leading to the radiator. damn i should have taken some pictures :(

what do you think is the problem? cylinder head gaskets, radiator, water pump, thermostat?

many thanks for your input and help!

best regards
Thermostat was not working and i had it changed but the problem persisted.

had the radiator checked and it was clogged thanks to a rusty paste which was inside the radiator.

had it flushed and repaired and now the coolant flow is ok.

the fan kicks in when required and works fine.

thanks very much for your help