How do I know if my thermostat needs to be replaced

What is your question?

There is a small amount of coolant under the thermostat housing on top of the transmission I had to add about a quart and a half of coolant could this be just the thermostat housing gasket or does it mean I need a new housing or thermostat and housing with gasket?

What makes this problem better or worse?

Better by adding coolant

How long has your 2014 Chevrolet Sonic had this problem?

Few days