If you're buying a new or used car, there's a good chance you're taking out a loan to pay for it. About 56 percent of new cars and about half of used cars purchased in the third quarter of 2017 were financed with loans, according to the credit-reporting agency Experian.

Those loans averaged more than $30,000 for new cars and almost $20,000 for used cars. 

But research by Instamotor, a car buying and selling website, as well as by Credit Karma and the Consumer Financial Protection Bureau, concludes that people taking out car loans don't always understand the fundamentals of auto financing, which means they could be paying too much for their loan. 

Here are seven misconceptions about car loans that you should know about.

It's the monthly payment that matters. While the payment must fit into your budget, if you focus only on that you could end up paying too much, says Bruce McClary, vice president of public relations and communications for the National Foundation for Credit Counseling, a Washington, D.C.-based nonprofit organization.

That's because you could be distracted from focusing on the total cost of the car, including the price and the interest charged on the loan.

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Jack Gillis, director of public affairs for the Consumer Federation of America and the author of "The Car Book," advises car buyers to compare the amount the dealer is asking for the car, plus the loan interest rate, to what others are offering. You can get that information on such sites as TrueCar and Kelley Blue Book. You can also compare car-loan rates by checking with banks, credit unions, and online lenders such as Clearlane and E-Loan

If the lender approved me for a loan, I can afford the car. It’s tempting to purchase the most expensive vehicle the bank will finance, but that’s risky. McClary says that you need to take a realistic look at your income and expenses to see whether you can afford the payments while having enough left over for savings and emergencies. 

Think ahead, too. Do you want to buy a home, make college payments for your child, or save more money for retirement? As a general rule, your monthly car expenses, including your loan payment, shouldn't exceed 10 percent of your gross monthly income, McClary says.

The rate on the loan from the dealer seems high, but it's non-negotiable. Unlike loans from your bank or an automaker, third-party loans arranged by car dealers often have rates that have been marked up to boost profits, Gillis says. Those rates, typically, are negotiable, he says.  

Before talking to a dealer about the rate, check with several local banks, credit unions, and online lenders to find the best rates you would qualify for, and then ask the dealer to beat them, says James Bragg, founder of the car-buying information website Fighting Chance. “Make the loan a competitive thing,” he says.

Put down as little as possible, so there will be more money available for other expenses. Not a good idea. The less you put down in the form of cash, a trade-in, or both, the more you'll add to the loan, leaving you paying higher finance charges, says Gillis.

Besides that, a low down payment also could mean that you'll end up owing more on your loan than the car is worth (because new cars depreciate quickly after being purchased). This situation, known as being "upside down,” can be a big problem if you need to dispose of the car, perhaps because you can no longer afford the payments. It’s also an issue if the vehicle is stolen or totaled, because your car-insurance company will probably pay you only what the vehicle is worth, not the additional amount you still owe on the loan. McClary recommends putting down at least 20 percent of the cost.

Refinancing my car loan isn't worthwhile. Sometimes refinancing can save you hundreds or even thousands of dollars. Even with interest rates being low in recent years, you still may be paying a relatively high rate if, say, your credit score was low when you took out the loan. Refinancing an auto loan is also much easier than refinancing a mortgage, and you won't incur fees. 

One important piece of advice: Avoid the temptation to extend the loan term beyond that of your original loan, advises Greg McBride, chief financial analyst for Bankrate. While a longer loan can further cut your monthly payment, the additional interest can offset some or all of the savings. 

The dealer says that if I trade in my car for a new one, he’ll pay off my existing loan. That might sound like a great idea, but unless your trade-in is worth more than the amount you owe on your existing loan, the dealer will simply add the outstanding balance to the loan for the new vehicle, essentially leaving you paying off two loans, says McClary. 

When my loan is paid off, it will be the perfect time to buy a new car. It’s just the opposite, says Gillis. “Now it’s time to enjoy your vehicle without payments,” he says. You'll no longer have the hassle of paying a monthly loan payment, and you'll save money by holding onto a car that's not losing its value as quickly as if it were new.