My car also has the only grille below the bumper. It is totally blocked now. Mine also had an air dam of sorts underneath just below the front of the radiator. I took it off. In addition to that, I now have a belly pan under the engine compartment all the way forward. I have no heating problems but just watch yours till you're sure. A grille block sealed properly is one of the sure fire methods for FE. You have a PM from me.
Wyldesoul 
Threaded Mode
