Does anyone know what the function of triangle shaped grill on the front dashboard of the '05 C230 is for? Is it a speaker, perhaps a woofer?

Also, where is the temperature sensor? Outside on the hood, or somewhere inside?

Thank you.

 

The grille on the dash is for a speaker. You can hear it if you put your ear up there next to it.
I'm not sure where the temp. is taken, but I can find out. Today in Phoenix, after parking the car for an hour, I got back in and the temp. reading was 127F. Highest I ever saw it! It went back down to 111F after I drove away a minute later. Hot, huh. That's what we get for living in a desert.

 

I have a 02 C230 coupe. In 02 the grill you are referring to also had an adjustable dial to change the air flow to the windshield. I ordered the BOSE system and there is also a speaker under the grill as well. To my knowledge the adjustable dial was removed in subsequent model years. It was probably overkill to have it since there is another dial further down on the dash that also controls the airflow.
Regarding the outside temp gauge sensor, I believe it is located somewhere under the front bumper and naturally cools off once the air flow increases as the car is driven.