Not long ago, standard auto loans had terms that ran 24 or 36 months. Then finance companies began offering 48 month loans, and they proved popular. So, why not keep going?

According to AAA, fully a third of new car loans made this year have terms of at least 84 months. That's six years of monthly payments.

Why are longer loans popular?  The answer is pretty simple: low monthly payments. The longer term loans allow people to buy a more expensive car than they could afford if they have to pay off the loan in two or three years.

But the downside is pretty steep. As with any loan, the longer the financing term, the more you'll pay in total. Unlike a house, which at least has the possibility of appreciating, a car's resale value drops as soon as you drive it off the lot. So, many buyers will be in for a shock if, after two or three years, they want to trade up for a new model. Like homeowners during the housing crash, they'll find themselves underwater, owing more on the car than it is worth. Caveat emptor. 

BONUS: Want to get the absolute best price on a new car? Consider buying it at Costco. According to Bloomberg News, the retail "club" sold about 400,000 cars last year, usually well below the lowest price one might be able to wrestle out of a dealer. Like everything else they sell, Costco negotiates with suppliers to lower their cost. And because they have revenue from memberships, they don't need the same profit margin as an auto dealer. Don't worry - Costco won't make you buy six cars all wrapped up together in plastic. Unlike almost everything else they offer, you can buy just one.