gtx 460 oc restarting after reaching 80 degree celsius

[papatalok]

my pc restarts after gpu reaching 80 degree celsius but my previous gpu gtx 260+ just doing fine.
gtx 260+ consumes more power than gtx 460 so the psu is not the suspect here.

my pc specs:
600w psu
core2quad q8400
8gb ram

 

[papatalok]

plus when the pc restarts there's no bsod appearing.
i already used msi afterburner to adjust fan speed to 100% but no luck, still restarts after 80+ degree celsius