I have read on
www.thailandguru.com that a farang legally cannot buy and own a car in Thaialnd, due to the protective laws in LOS.
The link is
http://www.thailandguru.com/transport-car-own.html
I knew that is was impossible to buy a land (only 30 years leasing contracts, except if you are American), but looks a little bit strange for a car.
I guess it would be possible to find some tricks, for example by putting the car on the name of a Thai people, but maybe some expats on this forum could give you more advices.