I wait till I have a car/vehicle and than go off my impression as to what IT is and its name. Like my Balt SS/SC, everyone thinks it would be a girl but definitely does not fit the personality the car has and thus is a boy, I was real original on the name though, Cobby

occasionally I pick on him and call him Pekacho(or however spell that damn pokemon name). I would say my cavalier coupe is a girl, its punny, no balls at all and a auto.
If I did get the new 'maro, it would probably be considered a boy aswell. Seems like a man, even was a boy autobot in that one movie