The official XU4 heatsink+fan is insufficient for the device. Even at full RPM, it basically does "nothing" to reduce temps. Heatsink lacks the surface area for the fan to have any sufficient effect.
Capping to 1.4GHz should keep temps under 80'c~, however, your high temps at 800MHz may indicate poor contact with CPU + heatsink.
The stock active cooler mounted on the XU4 is more efficient at dissipating heat away from the processor for most of use cases.
This is incorrect in my tests.
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