I am experiencing this same issue i will monitor this post.
MOBO:Crosshair V formula Z
CPU:AMD FX-8350 oc'ed to 4.5 Ghz apogee xl waterblock installed
GPU: MSI GTX 780ti stock clocks EK full copper water block installed
RAM: AMD Gaming ram 1866 4x4 16gb total with 12-12-12-32 timings
PSU: Corsair RM1000
when mine shuts down randomly i monitored the cpu and gpu thermals and right when the cpu hit 81c it shut down...automatically telling me the cpu saved itself from meltdown. but if i have it properly water cooled and applied thermal paste correctly what could be the issue? my homebuilt pc is about 1 year old and so is the pump,reservoir, water, and tubing.
thanks