fans not engaging machine shutting down

First why is your system running hot? What are you doing that’s stressing your system. The fact your system is shutting down is the correct action once the CPU has exceeded its safe temp level.

While your action of forcing the fan may appear to be a good thing you may have caused more damage! Let me explain when the CPU is overheating to this level for long periods the logic board PCB will start to breakdown as the epoxy decomposes chemically.

So what is the correct action here?

Using a good thermal monitoring app like TG Pro will give you a better view on what your thermal sensors are doing and you can log over time as well.

I would recommend first getting a good baseline before altering to much so you can see the improvements as you go through the steps.

I would clean off as much as you can from the drive as well as reduce the amount of apps loading up so you reduce the systems process load.

Did you try running the onboard diagnostics to see if any error popped? Restart the system pressing the D key. Some versions of firmware break the diagnostics so if you get an EFI error don’t panic as thats a known bug. Also give Safe Mode a try as well Shift (⇧)

Reference: Mac startup key combinations

First make sure the system does not have any dust buildup internally and the fan blades. Do you see any stains on the logic board?

The next action of change is to clean and re-paste the heat sink. Did that alter anything? If not then you’ll need to replace the heat sink.