Have you ever heard a purculating noise after you cut the car off? The radiator caps on neons are for crap. This is a known problem. A bad radiator cap will actually cause problems with the head gasket and head warping due to running hot. The cap allows excessive coolant to bypass into the overflow tank. This can be evedent by antifreeze on the ground that ran out of the overflow tank. The purculating noise is the coolant still boiling into the overflow tank after the car is shut off. A bad cap also does not allow the system to draw enough coolant back in the system on cool down. The result is that your cars cooling system eventually runs low on coolant which causes your car to overheat, possibly blowing the head gasket and/or warping the head. If you catch the bad cap in time you are only looking at about $7.00 and your car will not sound like an expresso machine when you park it.