Over time it is likely that your radiator will start loosing is fins due to corrosion. These fins greatly help the cooling efficiency of your radiator and without them your engine temperature will be higher than normal, even on relatively cool days. Depending on the rarity of the radiator you have 2 options, either buy a replacement of have the existing one re-cored.

Faulty car radiator

Close up of damaged and missing fins on a car radiatorThe 2 pictures here show exactly how the fins can start dropping, usually helped by the fan, hence the concerntration of missing fins in the area the fan covers.

The photo right show a radiator which would struggle to cool your car sufficiently. If you look on the Ground in front of the radiator you can see fins that have fallen off in a pile. Right is a close up of the worse affected area.