Well I went out last night,drove around the block and the mirrors were warm,and the air temp. was above the cold temp. warning.I thought I read somewhere that the cold temp. warning triggered the mirrors and washer jets.
So I guess the idea is that in the rain your mirrors stay dry,but spotted.They do work great melting ice and snow off though,by the time I get the car started,seat belt done up,get comfy,the mirrors are clear of ice or snow

 

i have an may 03' car. i guess i have never felt the mirrors to see if they are warm. but i thought i had read that in the owners manual they only come on when cold out. it would not make much sence to have them on all the time. i'll look into it.

 

Why does it have to make sense