For all you hoping the 806 does not have this problem, I can tell you it does.
I have had an 801 in the front of my car for a year without any issue other than it stopped logging gps data, not that bothered about that though.
I decided to upgrade the front to the latest 806, and move the 801 to the rear. I use the 32gb Samsung supplied with the 801 now in the 806, so I know the card is not an issue.
Yesterday I was driving into the sun and the camera chimed. I looked and it had just rebooted. After doing this a further six or so times, it went off and would not come on at all.
I tried connecting the power direct to the camera, no joy.
When I arrived at my destination, the camera was still very hot to touch. I tried connecting with a standard USB lead to my laptop, same result, dead.
I held the camera in front of the cars vent with aircon on cold for 10 minutes.
Plugged it back in and it started up as normal.
Today, in the morning, started up ok, after about half an hour, again driving into the sun, chimes and shut down again.
Once again, left it to cool down and it works ok.
This is with the masses of extra cooling holes in the 806.
Not happy. My 801 has been through hot summers and never done this.