1st make sure no leaves and crap are blocking the radiator if it's an a/c car make sure stuff isn't between the condesor & radiator. you could have a bad fan clutch, when the motor is hot and the engine is off IIRC the fan clutch should not spin freely, it should spin hard . If the fan clutch isn't working then just like an electric fan it isn't going to cool the motor. also make sure the radiator itself is in good condition, make sure the inside isn't crusty and blocking the flow tubes, this will reduce the cooling capacity of the radiator.