CPU would throttle down before shut down occur. I am afraid something is wrong with your unit.
Where did you read 85C ?
Do you have discrete graphic? It may get overheat.
The chipset may get overheat too.
I would suggest to remove the unit, blowing all the dusts, replace the thermal grease with Attic Silver, and install it back. If it does not help, then your heatpipe may be bad.