MacBook Pro still overheats after replacing thermal paste.

I am lost. I have a 2011 MacBook Pro that overheats constantly, no matter how small the task is. I have upgraded the HDD to a 500GB MX500 SSD, 4GB of RAM to 8GB of RAM, and reapplied the thermal paste with Arctic Silver 5. The MacBook Pro still overheats, even with the computer completely starting afresh in OSX 10.13.6. CPU temperatures spike up to 80ºC and fans fully spinning. Performance on the CPU doesn’t seem to be affected, although I could be wrong. Are there any other culprits that could be causing this, other than just a faulty CPU? Thanks.