I don’t think it would work Flu. (btw, I think it’s most Amex cards, not just Costco.) I tried it twice and it seems to vary by dealership. The Hyundai dealership where I bought one of my kid’s cars would only let me put $1,000 on Amex. I put $5K on Amex at a Toyota dealership. I suspect most have those limits because Amex charges really high discounts to merchants, in some cases almost double Visa or MC. Though they probably wouldn’t let you put the entire purchase on either of those either, their margins just aren’t that high. It was still good for the airline mileage.
