Many antifreezes are sold in pre-mixed 50-50 solutions already, but there are some of us out there that still make the mix ourselves. For those people, please make sure you don't have an overbalance of water in your mix. With too much H2O, you run the risk of the liquid freezing and absoultely destroying your engine. The best way to be sure is to flush out the system and replace it, before the chilly season comes.