[MetalMilitia]

It is almost certainly overheating. What you should of done is firstly cosulted the internet about how to remove the old HFS correctly. Secondly you should have removed the thremal pad completly and applied some good quality thermal paste instead. Im not sure what you tried to do with masking tape but its certainly not helping matters.

The core is the only part which needs to make contact with the heatsink as it is the only part which produces heat.

Speedfan will detect just about all of the heat sensors on your board. But it is often difficult to tell which is which so it may not be ideal. I would think your computer would crash before it does its self any serious damage so you shouldn't be in too much danger.

So basically what you need to do is pull off the heatsink you just stuck on, remove all the thermal pad, masking tape and crap. Then reattach it with a thin layer of thermal paste and some proper springy-screw thingys.