Ah more details :c)
There are a number of reasons cars can overheat but if you're sure you're not loosing coolant we can probably ignore leaks from pipes and radiators and probably head gasket failure (I presume there's no white "smoke" from the exhaust or excessive white gunge in the oil filler cap.
It could be the fan but I suspect more likely is that the coolant system and with age has got a bit gunked up - especially the radiator.
Probably needs flushing
http://www.popularmec...o/maintenance/1272246
If this doesn't work I'd suspect a water pump on it's last legs