Borrow From a Bank, Credit Union, or Finance Company

Banks and credit unions usually offer set, nonnegotiable rates, often less expensive than dealer financing. (They are also less likely to push the unnecessary expense of credit life insurance, which ensures that the loan will be paid off if you die prematurely.)
Membership credit unions that offer auto loans typically offer lower rates than banks and finance companies. But finance companies -- often the most expensive of all -- may accept borrowers who are greater credit risks.
In 1991, the IRS eliminated the income tax deduction for interest on most personal loans. The major exception is interest on a home equity loan, which is tax deductible on principal up to $100,000 no matter how you spend the money.
Some banks now offer "tax-smart" loans to give back the car-loan deduction to consumers. A tax-smart loan combines the ease of a regular auto loan with the tax deductibility of a home equity loan. With a tax-smart loan, you do not have to go through the closing procedures and expense required by a regular home equity loan. And you can usually borrow up to 100% of the equity in your home. Unlike a regular home equity loan, the primary collateral on a tax-smart loan is the automobile. To earn the tax benefit, a lien is placed on the home as well.
While tax-smart loans may be smart for the bank that offers them, they may not be such a great deal for the borrower. A tax-smart loan is safe for a bank to make: it has the security collateral of both your car and your house. The bank usually charges the same interest rate on a tax-smart loan as on a regular auto loan, which could be significantly more than the rate charged on a home equity loan.
Not only are you tying up the equity in your car and home for this loan, the savings you realize on the tax deduction may be less than the money you save with a lower-rate loan.