Can I only drive in Costa Rica for 90 days

As an American citizen, you are not required to apply for a separate 'visa' to enter Costa Rica in advance of traveling, but you will have to exit CR to renew this visa, within the time period shown on your passport, although there is no guarantee you will be given 90 days. It could be 9 or 90 days.
You can't get a CR drivers license until you are a legal resident, which could take a year or more. Even after receiving your 'comprobante' which essentially means your application is 'being considered by Immigration, so you are no longer required to exit CR, to renew your tourist visa unless you wish to continue driving. So be prepared to exit/enter many times ... 

So, you can bring in a vehicle and continue to drive, but you have to follow these rules.
Realize that vehicles are expensive here, due to these high import taxes which in turn will mean the cost of purchasing a vehicle is expensive..

Thank you

Hi everyone,

Please note that i have created a new thread on the Forum Costa Rica with your posts for a better interaction.

Thank you

Stéphanie

K. is absolutely right. If you don't leave you will be driving with an expired license and subject to penalties and if you have insurance it will - as far as I can tell - be invalid. Some say "I'll just risk the penalties" but the penalty can apparently be the impounding of your car; plus the insurance thing I just mentioned. Which means you have to leave every 90 days if you want to legally drive. Which sucks. But that's how it is.

posted twice for some reason; ignore this post

Panama has the same requirements in that you have to leave the country to renew drivers license to keep it legal.

The penalty for driving on an expired license is 50,000 colones.