Update posted by texasfan1528(CA) on January 16, 2011 at 12:50 PM
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Antifreeze not only lowers the freezing temperature of water but it also raises the boiling temperature so that your coolant doesnt boil away. The radiator cap also has the same effect where the cap works as a valve and holds pressure also significantly raising the boiling temperature. So my guess is that before you added antifreeze again or changed the cap (whichever one was the culprit), the water in your coolant was boiling too fast and as a result causing your car to overheat. If thats the case, i would recommend using a higher antifreeze/water ratio. Doesn't matter if you live in CA, the antifreeze still makes for a better coolant.
