Blocking that lower portion won’t help the car warm up, that’s the whole point of a thermostat.
When one drives in very cold ambient temperature, it is not unusual to have to cover grille in the winter.
I understand the function of thermostat.... but it ONLY works if the engine is generating enough heat. At very cold ambient temperatures, the thermostat NEVER opens. Instead, the engine-computer forces the RPMs to remain over 1800 all the time while driving in an attempt to generate enough heat to warm up the xMission.
The xMission case is a HUGE hunk of aluminum which dissipates heat into the surrounding air. When ambient temperature is below 0f, the engine struggles to bring it up to operating temperature.
I have done many experiments over the past 2 winters and when ambient temperature is very low, the xMission sucks too much heat from the cooling-system. If the cabin-heat is turned on, the engine RPMs remain above 1800 all the time while driving. This is the engine-computer responding by trying to generate enough heat to bring the xMission up to operating temperature.
In other words, when ambient temperature is very cold, the engine cannot generate enough heat for BOTH the xMission and the cabin. This forces the thermostat to remain mostly closed.
When I cover the airflow into the radiator, this all changes. The engine generates enough heat to bring xMission up to operating temperature WITH the cabin-heat turned on. This allows engine RPM to fall into 'normal' operating range.
