Although you may want to offer your services as often as you can in order to make management happy, there are certain things outside of the office you shouldn't engage in. You can be friendly to your coworkers, but there are several aspects of interpersonal relationships you should stay away from. Fixing your supervisor's car may seem like a good career choice as he or she may hold you in higher esteem afterward, but it could wind up blowing up in your face causing a great deal of drama.
1. Skills - While you may want to help to the best of your abilities, you may not have the skills to accomplish your goal. If you were a good mechanic that would have been your career choice and at this point fixing the car isn't such a big deal. However, you could be lacking important knowledge needed to fix the car if you don't have a background in auto-repair. Then you run the risk of causing more damage than there was initially. Your lack of skills could make for a very terrible situation and you could become responsible for anything that goes wrong. The ripples in the employment pool will begin to form into waves.