Hi, Logan.
There are several reasons for overheating. One is a malfunctioning thermostat (they can jam completely shut, closing off all circulation...which makes it overheat in a hurry). I can't imagine one getting stuck and then miraculously working fine...but stranger things have happened.
The most common one on BMWs is the poorly functioning fan clutch. When that goes, the car will do fine going 40 or 50 miles an hour, but it overheats when you're stuck in traffic, not moving.
The other reasons are stuff like bad hoses, but you'll see them leaking, have steam coming out from under the hood, stuff like that, so those are easy to diagnose.
I don't see how BMW can have it both ways, i.e. they found nothing wrong with the car, yet admit that it overheated (since that's the reason they claim not to have to fulfill their warranty obligations).
One thing you might want to check is the information stored in your car's computer. The computers in some fancy cars store information from every moment of the car's operation. I got caught when I took my mom's cadillac to the dealership for warranty work. They knew I'd burned out three times, maximum braking three times, and hit the top speed limit three times...they also knew at exactly what time I'd done those things.
I would ask for the printout, or however it comes, from your car's computer. That would show how long the car was operated while it was hot...which might help or hurt your case. If that computer readout shows the car overheated for 4 minutes and you pulled over and took action, and that the temperature was fine during the 10 minutes you drove to the dealership, that would support your case and make them look like swine. If the printout shows you drove for 30 minutes until the car wouldn't run, you're screwed.
I would also recommend checking out your dealer on this web site:
http://www.dealerrater.com/dealer/de...sp?dealerid=58
That'll tell you if anyone else has been burned recently, or if they have a good reputation for being fair.
Definitely, continue making yourself a pain in the ass. Threaten them with a lawsuit, have an attorney write a letter, whatever it takes...you've got 12 grand at stake.
Flunky
PS-Don't forget, you can also threaten to leave a nasty review on dealerrater...which would cost them tens of thousands of dollars of sales...the Dark Side, Luke! Use it!