My 2000 chevy. Impala is overheating still after replacing the the thermostat, hoses, and water pump. My head gaskets were replaced about 6mths ago and we checked for cracks again and nothing. We've checked the oil its not milky. My low coolant ligh thas been on for 2 yrs now but its overheating also checked the radiator and that's ok what could it be?