Hot 400E, not in a good way

[Landon]

Hi,

just got a 400E and drove it to Austin from Dallas (200 miles) and to work and back, waiting in traffic long enough to get it hot...let my wife take a test drive, and it comes back in 15 min with the temp guage in the red. She did not drive it hard. Opened the hood and found the cap blown off the coolant tank. We kept it running, aux fans and heater on, and a hose on the radiator, got it to cool down a bit. Turned it off, then back on, and it started out around 85C and went right back up towards the red. The coolant tank took about 3 quarts. So two possibilities, stuck thermostat, or an air bubble in the engine...are these good diagnosis, and how do I bleed the engine?
Thanks for any encouragement.