Never borrow money to purchase a car.
(As with all heuristics, there are exceptions. For example, if you can get finance at rate that's lower than the rate of inflation, or even what you'd get from a savings account. It's likely to be better to invest your money elsewhere at a higher rate of return. So long, of course, as the loss that the dealer/financier/manufacturer is making on the finance isn't baked into the price of the vehicle!)