Derogs stay on 7 years from the date they occured.
Accounts themselves report for about ten years after they're closed.
So your auto loan will stay on your report for about ten years after it was closed. If it was paid off in, say March 2010 - then it would stay on your reports until about March of 2020. And any baddies or derogs on that account will age off seven years after they occurred. So if you had a baddie in, say September of 2008, the baddie would report until about September of 2015.
In that scenario, the baddie would have aged off in 2015, but the account will continue to report until 2020 giving you about five years of reporting a "good account".
When car dealerships pull your credit report, they can see what you can see. If they run an auto-enhanced FICO score, the score will weight auto accounts a bit more heavily; but they are scored on the same CR's as your standard FICO score.
Hope that helps!