Where to go next with my repair.

I have been teaching myself how to restore the Fat PS3. This is my first try in repairing this type of console.

Recently, I have taken apart a reverse compatible CECHB01. Before my repair attempt, i plugged power and HDMI in, pressed the power button and all that would happen is the Red light would go green and then back to flashing Red (No yellow or blue.) So i cleaned all the dust out, hit the cpu and gpu lids with a heat gun for 30 seconds each on high, put fresh mx4 on the cpu and gpu lid and closed it back up enough to test. It now turns on!! However, the fan ramps up high after 10 minutes of playing a game (dark souls) but is fine when not playing a game. (Maybe bad GPU?)

I don't want to burn this console out, so it goes back on the shelf for now. I do not know if this is normal due to lack of experience.

What should be my next move? Try de lidding the cpu and gpu to thermal paste under those before i will get adequate cooling for each? Im feeling the the NEC tolkens are fine if it is running right now. Is the fan supposed to ramp up so fast? Is it fine and i just do not know it?