I have the same problem (not over heating but xorg now constant spinning). Prior to upgrade from 16.04 to 18.04 never had this issue. At first I thought it might be related to application but even when nothing is running the x server just spins.

A small detail - I actually have a 2500K but there was a regression in the xserver with 18.04 (16.04 worked fine but 18.04 cause a bug that existed in 14.04 (I think - i had this problem after 12.04 I think but it was a long time ago) to reoccur and the intel graphic would cause crashes) so I purchased a R72402364P - anyway an strace shows this small tidbit with the xserver spinning):

(I filtered out other stuff the xserver is doing but as you can see from the timing it is spinning on ioctl calls):
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1540153775.186129 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3f50) = 0
1540153775.186613 ioctl(16, DRM_IOCTL_RADEON_GEM_CREATE, 0x7ffd14ed45c0) = 0
1540153775.186650 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed45a0) = 0
1540153775.186690 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed4650) = 0
1540153775.186723 ioctl(16, DRM_IOCTL_GEM_CLOSE, 0x7ffd14ed4648) = 0
1540153775.186757 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed4650) = 0
1540153775.186788 ioctl(16, DRM_IOCTL_GEM_CLOSE, 0x7ffd14ed4648) = 0
1540153775.186818 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed4650) = 0
1540153775.186849 ioctl(16, DRM_IOCTL_GEM_CLOSE, 0x7ffd14ed4648) = 0
1540153775.186993 ioctl(16, DRM_IOCTL_RADEON_GEM_WAIT_IDLE, 0x7ffd14ed46e0) = 0
1540153775.187389 ioctl(16, DRM_IOCTL_RADEON_GEM_CREATE, 0x7ffd14ed45c0) = 0
1540153775.187425 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed45a0) = 0
1540153775.187460 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed4650) = 0
1540153775.187492 ioctl(16, DRM_IOCTL_GEM_CLOSE, 0x7ffd14ed4648) = 0
1540153775.187611 ioctl(16, DRM_IOCTL_RADEON_GEM_WAIT_IDLE, 0x7ffd14ed46e0) = 0
1540153775.188095 ioctl(16, DRM_IOCTL_RADEON_GEM_CREATE, 0x7ffd14ed45c0) = 0
1540153775.188130 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed45a0) = 0
1540153775.188264 ioctl(16, DRM_IOCTL_RADEON_GEM_WAIT_IDLE, 0x7ffd14ed46e0) = 0
1540153775.188579 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188605 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188628 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188652 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188675 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188698 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188721 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188744 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188768 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188793 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188816 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188840 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188863 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188904 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188930 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188953 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.188977 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.189000 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.189024 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.189047 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.189071 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.189094 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.189118 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed3df0) = 0
1540153775.189323 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed4150) = 0
1540153775.189363 ioctl(16, DRM_IOCTL_RADEON_GEM_BUSY, 0x7ffd14ed40f0) = 0
1540153775.189417 ioctl(16, DRM_IOCTL_RADEON_GEM_CREATE, 0x7ffd14ed45c0) = 0
1540153775.189451 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed45a0) = 0
1540153775.189487 ioctl(16, DRM_IOCTL_RADEON_GEM_VA, 0x7ffd14ed4650) = 0
1540153775.189518 ioctl(16, DRM_IOCTL_GEM_CLOSE, 0x7ffd14ed4648) = 0
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