Andrew, The water went somewhere. If it's so low that it wouldn't come out of the bleeder screw, then you may want to look for a cracked freeze plug. But, first I would refill the system and bleed out the air and watch it closely. See if it happens again. How long did it take to get that way. When was the last time you checked the coolant. If you haven't replaced the thermostat, then I would. If it stuck at some point and you didn't notice it, then it may have made the car boil over and loose most of the coolant when you didn't notice it. John Hervey http://www.specialtauto.com/engine.shtml << Recently I encountered my first overheat problem, so I figured I'd probably let the coolant level in my tank get too low and sucked up some air. Following a procedure discussed here numerous times, I attached a rubber hose to the nipple on the bleeder screw, started the car, let it warm up, then loosened the screw to let air out. To my surprise, nothing came out at all. I loosened the screw to the point of removing it entirely. Nothing. No water, no air. >>