Can I buy car with retirement visa in thailand?

Yes you absolutely can ! Most expats on retirement visas in Thailand are quite open to the idea of buying a car mainly because the prices of vehicles in Thailand are affordable and it will help you to travel to the places you wanted to go.  You only need a copy of you passport, visa and entry stamp, and a certified copy of your address from your nearest immigration office. Maybe you already know, but be very careful when choosing a second-hand car, many have been to the moon and back and have been 'clocked' and revamped to look like new!