I topped off my car with water/coolant to the max needle point and after I drive my car for like a week I check the coolant in the morning to make sure it's good when the car is cold and the needle is all the way down every time. I thought it was a leak but when I unscrew the bleeder screw it sucks in air and the needle slowly rises back up to the max point. When I topped it off I did follow the instructions as to opening the bleederscrew and turning up the heat. Could it be because I've used almost a gallon of tap water?***128543; Any answers would be appreciated thanks!