I just did a coolant flush last week. I was having troubel getting the water pump to start the venting process, but it eventually did it. The car was running fine for about 3 days. Then on the fourth day after driving for about 20 minutes on highway the overheat light came then quickly turned red. I put an OBD scan tool on the car and no codes came up. I belive its the water pump, but is there any way for me to verify this before droping $500 bucks on a new pump and thermostat? Could it be anything else?