New research from Carfax found 3.5 million used cars are currently for sale in the U.S. with unfixed safety recalls. There are about 300,000 in the state of Texas alone, according to NBCDFW.

Recalls work like this: When NHTSA receives enough complaints about a problem, or a serious enough complaint is made, an extensive investigation takes place. A recall is issued if an engineering analysis proves there is an inherent flaw in the vehicle's design. NHTSA then works with manufacturers to ensure customers are notified. Often several letters are sent over the course of a few years. Ford, for instance, told NBCDFW they send out five notifications over four years to warn customers about recall issues. The owner then takes the car in for a free fix.

The problem here is that the owner is not required to have the work done nor are they required to notify a potential buyer of the car that the work was never completed. Thus, major repairs can be overlooked when buying or selling a used vehicle. With the current fleet of cars on the road the oldest in history, dangerous problems potentially go unfixed for years.

If you're concerned your car may have been recalled under a past owner, Carfax provides a service for looking up recalled vehicles free of charge. All that you need is the car's 17-digit Vehicle Identification Number. By August, a NHTSA ruling last summer will go into effect requiring all major auto and motorcycle manufacturers to also provide consumers with a searchable recall database.