BTW what should I do to put CD's with mp3 files readable in old car cd players?
Ain't gonna happen, friend. You need a cd player that can read mp3 files. The only thing you can do is burn CDs with the mp3 files turned to WAV files. You lose loads of space and some audio quality doing that though. Your best bet is to either get a CD player that reads mp3 files or using your phone/aux jack and an mp3 player.