well if the temp stayed normal i'd say your all right. And you didnt notice any lack in performance so you should be fine. warping heads and blowing head gaskets is when it starts over heating or revving to high in the case of a HG. i wouldn't suggest running the engine low on coolant like that though because it can do bad things if you temp starts rising. risking the engine over a 150$ rad isnt a smart thing though.