Hi Philippe, If you have a car with a proper radiator ( like our old Chryslers ;o), you're actually better off with water and anti-rust in the summer than with water and ethylene glycol. That's because water has twice the specific heat capacity of ethylene glycol. If you've got one of these new cars with a toy radiator, then you have to use the water-antifreeze mixture because the coolant temperature has to be higher than water is reliable at to dissipate the heat in the cheapie radiator. ( Fortunately I don't own any cars newer than my 300G! And all the rest are old Chrysler products too! ;o) Also a eutectic mixture of water and ethylene glycol actually has a LOWER freezing temperature than straight ethylene glycol. It's about fifty-fifty but I don't remember the exact ratio right now because it never gets that cold here and I only use 25 percent in the winter here. The Prestone jugs used to say what the proper mixture is but then they discovered that they sell more antifreeze if they don't! As for your freezing experience, you were just lucky that the temperature wasn't cold enough to continue freezing the water before it warmed up for the day again! BELIEVE ME, they are EXPANSION core plugs!! Kurt Kurt Greske ( kurt_greske@xxxx )