I assume it has the "wonderful" extended life antifreeze in it? That stuff is terrible, causes the aluminum to corrode if exposed to air. Try replacing the radiator cap and the reservoir cap. Also, don't pop the radiator cap off to check the level, even if your reservoir is the black plastic one you can't see through. You probably have a low coolant light that will come on if it empties.
I'd reccomend you flush the radiator and engine and fill it with the good ol' green stuff