OK another update, I have been trying to work out if the heat output of my replacement CPU matches the normal heat output for this model and replicated a bench of the NH-L12 on Tom's Hardware cooling a 4770K overclocked and undervolted and running Prime95 at 4.0GHz. The results show the same deltaT 47°C between CPU and ambient indicating similar heat output because the deltaT would be greater if the CPU was running hotter with the same cooler. This is quite a neat proof as the figures did match exactly so I am satisfifed this CPU is working to spec.
Thanks to all those who contributed.
For those who are having similar problems...
- my conclusion is that the first CPU was overheating as the replacement CPU is running significantly cooler.
- So this means there are faulty overheating CPUs out there and it is worth exchanging them if you have one, but this is happening in the context of a CPU type which does run hot in bench tests and requires some BIOS adjustment and a better cooler than the Intel retail cooler to bring the temperature closer to spec (Tcase 72.72°C) under heavy load but it still tends to exceed this even under coolers with an appropriate thermal wattage.
- FYI The two key BIOS adjustments I made to enable this cooler were
- to set the power limiter somewhere between 88 -125 W, currently 110W
- and to set a negative vcore offset of -0.050v.
- These restrict turbo to 40x in Prime95 v28.5 but allow it to run steadily and keep the temps close to Tcase.
For Intel these facts indicate a quality control issue. Further to this, with a non faulty CPU, using the retail cooler results in thermal throttling under load and the CPUs are not able to operate to spec either in terms of operating temperature or clock frequency under loads like Prime95 v28.5 with third party cooling like the NH-L12.
This suggests to me IMHO that the package thermal interface relies on thermal throttling to prevent CPU damage rather than providing a sufficient pathway for peak heat transfer, by design. As a result the CPU cannot achieve its specified capability in bench tests like Prime95 without third party cooling capacity significantly exceeding the rated thermal output of the CPU.