Sold car and it broke down on buyer?

Located in Ontario, by the way.
I bought a 2001 Honda Civic about a year ago, i had a new motor, new starter, new alternator, and new battery all put in the car and put some rims that I 3 grand when I bought them on it. It had NO signs of problems after all the work. About 4 months later in the summer my cousin offered to sell me his Mustang so I wanted to sell the Civic. A guy about 18 years old looked at it by himself, then the next day looked at it with his dad, I even let his dad test drive it and they were excited and loved it. I sold it for $2500 (cheaper than my original asking price because the body isn't perfect).
Two weeks later I get a text that the car overheated and he was stranded because he drove the car all the way across the border to the States! It's been a couple months now and he's taking me to small claims. The bill of sale says as is, and we both signed it, both have a copy.
The car showed no signs of problems with me and I don't know if he had the car inspected before driving it to the States.
What should be my course of action? The car was great when it was in my possession

Try to get evidence that he kept the car for more than a dday.sold as is = sold as is no way around it, good luck

Unless a warranty is offered in writing, all car sales are automatically considered as-is.

He will get nothing. Respond to the lawsuit, though. If you ignore it, he will win by default.

It doesn't matter that the car was great before you sold it. He bought it. It's his problem after that.