Replaced the Leaking water pump on my GTP. This stopped the dropping on my driveway. Ran the car for 1 hour and no leak. Then I drove the car 600 miles and my low coolant light came on. Needed a half gallon to fill it back up. I did check the Coolant level after I replace the water pump to make sure the radiator and res were filled 3 days in a row. My Oil is clean. Any Ideas