Q&A

I changed the thermostat and the radiator fan is still blowing cold air when the gage is showing hot. Sometimes when the fan goes on it is blowing hot air off the radiator and that is when the gage is showing the temperature to be in the middle like it should be.I also got the sensor on the engine changed. I was told the relay is working fine.
What is my next step to be? Could a new thermostat be faulty?