CPU overheating while idle

Hi
My Alienware 17 seems to be having CPU issues. (i7 4910MQ)
I noticed it was running hot with cores peaking at 100 sometimes, like just now when i started streaming video from my laptop to xbox via DLNA server the cores went nuts at 90-100c. the machine was built in 2014 so its starting to age a little but otherwise runs great. now as i write this the temps are back in the mid forties after turning off the video stream. 

this problem has persisted alot but just now has gotten alot worse (this is the first time its hit 100)
Things ive tried:
• using a cooling mat
• tilting the cooling mat to 45 degrees
•cleaning out the vents
• repasting the thermal paste.

this is the paste i bought
Halnziye HY610 Gold 30g Tube Thermal Grease Paste for CPU Heat Transfers etc | eBay 

Is it time to replace the cpu? or can i try something else?