Threats to sue me

Im from Alabama. I sold a car to a guy in September and took a 1000.00 down payment and let him drive off with the car. The terms were that i keep the title until he came back at the first of October to pay the 500.00 he owed. He did and i turned over the title, he drove the car two weeks before he paid it off. A week and a half ago he calls me asking if i had problems with the car, i said the only thing it done with me once was run hot. i put water in it and it was fine. He said he was going to have to do some work replace a few things that it was running hot and had started a week after he paid it off. Hes been driving it for over 3 months. A week later he calls me and says hes got a lawyer and that he was going to sue me unless i gave him his money back on the car. That knowinly I sold him a lemon. Im not a dealer, its a used car. Can he really sue me for that and win a settlement. Thanks for any help.