Car loan rates have increased as the fed rates hav increased, so the spread here is much smaller. If you were buying a car a couple years ago when you could get 2% or less loans, this idea makes more sense.

But the more broad item you are missing out on is called sequence of returns risk. So if the only way you can do this is by needing to cash out the investment monthly to pay the loan, then it likely isn’t a good idea.