Is getting hot, I just changed thermostat and I drove over 30 miles and once I park and car is idling, it began to get hot. What else could the issue be? Or what could I do?

 

I assume the engine temperature, as seen on the temperature gauge on the dashboard shows the engine getting hot?
If it only gets hot at idle then perhaps the radiator fan is not kicking in. When the temperature goes above what you'd expect does your radiator fan come on?