[outtamymind]

the radiator if it's curved as you say is cracked and needs to be replaced. and yes there is no actual rad cap as the cobalt coolant system is more or less a sealed system. the correct way to top it up is through the res cap. also make sure you are using a 50/50 mix of dexcool coolant. so pink stuff not green stuff, mixing will cause some nasty gunk to form up and potentially cause some damage