In an earlier thread on this topic, (which I can't find right now but I know it's there), several people stated that they paid for the entire car with a credit card. While the dealers weren't too happy about it, they accepted the payment. One person wrote that the legal department of Visa stated that no company that accepts a credit card for one type of payment, service department, for instance, cannot then say that they will not accept it for sales. Additionally it was stated (where is that thread?) that Visa legal noted that no company can say they will only accept a certain amount and nothing above that.

I will be buying a car soon and I will be testing this out as I want to put the entire payment on my card.