@Feins
As a temporary fix you could try setting processor affinity to fewer cores. Obviously this is not ideal and would slow the transcoding down but it may allow your CPUs to run cooler.
Start Task Manager/Processes. Right click on the tempgenc process, choose set affinity, and check/uncheck the cores.
@cutterman
Thanks for the suggestion as its like having a Bugatti Veyron with a W12 engine and crippled 6 cylinder to have it run at W6. I can achieve what you suggest using parallel which has the limitation to support up to 8 core and 8GB of ram.
Ive start a new thread here https://forums.macrumors.com/showthread.php?p=11626446#post11626446
as its not nice to hijack someone thread as this is out of the topic as well.