Overheated to 250, died on side of highway, left stranded

[986_inquiry]

Car would get to ~210, flashing light, last few months

Mechanic checked temps, says everything seemed ok

Replaced cap to .04 did not help

Mechanic said maybe low, fill to top, any overfill will boil over, do no harm

Did that. Temps went to 250 in 5 miles, ac stopped workin, solid red temp light. Mechanic said shouldn't be, bad temp gauge? Drove 5 miles, temp dropped to 180, light flash, AC working. Drive 5 more miles, temp to 250, AC stop, solid light. Downshift to get off highway, everything died, all instrents lights on, hear clunking sound. Get out, light smoke coming from the back. Boxster will not restart, stranded, waiting for tow truck now.