1999 Chevrolet Camaro Z-28 low engine coolant light

1999 Chevrolet Camaro Z-28 V-8 mileage: 60,000. I'm getting a low engine coolant light on my dash lighting up. I've followed the directions to put coolant in. Bled the two valves etc, poured in coolant, ran the engine, etc. But I'm still getting the low light on in the dash. The radiator is filled to the brim. Maybe I'm not bleeding the valves correctly. I don't see a leak; the car is clean underneath. Is there something special to do to add coolant in a Z-28? Thanks