I lifted the car yesterday to check, much to my surprise, the brand new thermostat (Behr OEM) was leaking from the bottom. The leak was very slow, not sure if it was a leak or the gasket setting in or over torque. I just don't know what went wrong with the new thermostat.

I am wondering, when fitting the new thermostat, should the thermostat housing plastic body touch the engine metal body? Or should there be a hair line distance between the two and the gasket seals that gap?