CMIIW but I think that they no longer allow you to claim the full value as a tax deductible donation, only the actual sale price that the charity gets when they sell the car.
That is only if the charity resells the car, if the car is being used by the charity then you can claim the full market value.
See here:
http://www.foxbusiness.com/personal-finance/2011/12/14/irs-and-insurance-rules-for-charitable-car-donations/ 2. Doing the math on your deduction
For cars that will simply be sold for cash, you are allowed to deduct only the charity's sales price of the car--not the vehicle's market value. Your deduction is further limited by your marginal tax rate. For example, assume a charity sold a vehicle you donated for $3,000. If you were in the 28% tax bracket, your deduction would be capped at $840.
But you can deduct the full market value of vehicles that will be used on an ongoing basis by a charity for things like deliveries. So if you give away a car that will be used by the charity, and it has a fair market value of $5,000, your deduction will be $1,400, assuming a 28% tax bracket.
Regardless of how the car is to be used, be sure to get a receipt from the charity. If the charity sells your donated vehicle, it is required by law to send you a notice of the sale within 30 days advising you of the car's sales price.