I'm hoping someone with industrial design experience would answer this, but it doesn't look like anyone has yet, so I'll do my best, as I would if one of my art students came to me with such a question.
I think your combination of interests is wonderful, and it sounds like you have a good sense of where you are going with your education and your future career. Engineering and Art is a great combination, which not everyone can do! Congrats, that is an important step in your future. I hope you have told your mechanical engineering professors about your interests in art and a future career as an industrial designer. They may be more focused on the engineering aspects of your future, but I'm hoping they will be very interested and might have some advice or contacts for you. I would encourage you to find some internships with industrial designers or companies during your summers. You make take a look on line to see if there are any professional organizations for industrial designers you could join.
You might also want to check out the Museum of Modern Art (New York) website; they have a design collection (all created by industrial designers) that is really wonderful. Also, why not keep a running list of industrial design projects you really like--furniture, cell phone designs, car designs, and so on. (This is what I would suggest to anyone thinking of a career in the arts; notice what you like in your potential art field).
In the meantime, keep your grades up and work on your art portfolio. Take as many 3-D art and craft classes as you can--sculpture, ceramics, fiber and so on. Be sure to include some sketches or preliminary designs in your portfolio, so future employers can see how you work; how you think, how you problem solve, how you find solutions and so on.
Until a real industrial designer comes along, I hope some of this has been helpful, or maybe it has reinforced what you've been thinking about. Best wishes.