Cars, like people, are temperature sensitive, and that is why your car has a thermostat. The thermostat housing covers and protects the car's thermostat to make sure it can keep the engine running at the right temperature.
It is important to replace your thermostat housing immediately if it is damaged. Even a crack can mean a thermostat that does not work right. Make sure to find the thermostat housing that is appropriate for the make and model of car you drive.