Do men think a girl who knows how to do the basic car mechanics/maintenance is less feminine? is it a turn off?

To me, any female who is competent has many pluses going for her. A woman who can do things that men traditionally do is, I believe, fascinating. And I personally wold prefer a woman who could change a flat tire over a woman who couldn't...all other things being equal. Competence is a turn on. This is the day of women doing what men do, and many times doing it better than men. So go for it, and if you can work on diesel trucks, let me know.