1. When the car becomes 13, just before/when major things start to go wrong with it, it's the best time to get rid of it, and do a Mitzvah to your pocket.

2. donate a piece of junk car to a Jewish charity organization

when one non-jew is in the car alone with three jews. By doing this he undergoes a car mitzvah and is officially jewish

The act of donating an old junker car to your local Jewish charity.