Q: Thermostat housing leaks coolant

Hello. The thermostat gasket is most likely what is causing the leak. The gaskets overtime become hard and lose the ability to seal the coolant passing by the thermostat. The replacement of the thermostat and gasket is the most prevalent fix. It could also be a crack in the plastic structure of the thermostat housing which is causing the leak. I suggest having the cooling system pressure tested by a well trained technician. Pressure testing the system will expose any coolant leaks. A properly trained technician would be able to inspect the coolant leak and make the necessary repairs to have your vehicle running smoothly again.