I think this is a grand idea, for a couple of reasons.
1. You are 17, and in most States, it is not only impossible but illegal for you to enter into a long term loan contract without consent and co-signing of your parents. In fact, even then it is highly improbable. More likley, your parents bought the car on THEIR credit and you make some payment to them or the bank directly.
I don't know that part.. but I do suspect you don't actually OWN the car. They do.
2. You are 17. You should have ONLY a part time job. Your main pritorty should be school, not working 40 hours a week at a ****ty, dead end job. There is no way you are a mechanic.. you are probably a low end tech slinging tires. Hopefully the kind that actually checks to see if you pulled the old oil filter gasket OFF before you put the new one on.
Your number 1 priority MUST be school. You like working on things? Get a degree in Engineering and go build massive projects. I literally threw up when you were talking about how OK a 400 dollar a month payment was.. for you... a 17 year old... boy.
400 dollars a month is 2 what I pay and I make a **** ton more money than you. At 17... the reason we make it hard, if not impossible, for you to get a loan on your own is because of just how stupid we can be at this age.
At 17, saddling yourself with debt for a shinny toy on wheels is literally the stupidest thing you can do and NO ONE and I MEAN NO ONE over the age of 21 will think this is a good idea.
Only 17 year old thinks this a good idea...
Take a word of advice from someone much older and successful. Don't go into debt until you actually know what that means, and never for **** you don't need.
Debt can kill you and it can cripple your life.
Go to School. Stay in School. Get a degree that MATTERS and will make you money. No history, no soft science bull****. No English or philosophy. No Sociology UNLESS YOU DAMN well intend to get a Ph.d and start a practice.
You want to work on stuff? Build stuff? Be the smartest guy in the room with the best toys because you make bank? It isn't slinging tires and blowing off school... its going to a good school and getting an engineering degree or other advanced science/tech.
My .2 cents....