there not a must in ur area, just helps in keepin the engine warmer when real cold

i guess for people more north i guess.

I made a plexi cover for my cummins with a 6in hole in the center that fit in front of my radiator for last winter. Made a big diference in the heater function. Without it the heater wouldn't blow warm in my 15 mile drive to work. I had heat within a few miles with it in.

did the motor run hotter?

No more than what it runs in warm weather. If you make one make sure you put a hole in the center. I read things about them not having a hole in the center it puts a lot of stress on the cooling fan. And make sure you put it between the radiator and the intercooler. A friend of mine made one out of a heavy sheet of cardboard from an exhaust box and it held up all last winter.