
Originally Posted by
OTEP
The OEM radiator is a combination of plastic and aluminum.
The top is plastic because its supposed to destroy itself in the event of an overheat (sort of like a fuse for the cooling system). Otherwise, the pressure will relieve itself at the next weakest point. Which is usually the [very expensive to replace] cylinder head gasket.
Your past overheat may not have been due to the radiator having a plastic component. It just so happens the radiator sacrificed itself to save the engine.