It may sound counterintuitive, but paying off your car loan probably won't improve your credit score. In fact, if it's the only installment loan you have, your credit score could take quite an unexpected hit. Here's why: According to the Fair Isaac Corporation, creator of the mighty FICO score, the types of credit consumers use (otherwise know as your "credit mix") accounts for 10 percent of their overall FICO score. In order to maintain a top score, consumers need to show that they can responsibly manage various types of open credit lines including mortgages, installment loans, credit cards, and retail accounts. So if your auto loan is the only installment loan you have in addition to a few credit cards, making that last payment or paying off the loan in a lump sum could really hurt your overall credit mix. In some cases, consumers have even reported a drop in their score of 50-60 points, thus disqualifying them from receiving the best interest rates on mortgages or other loans.